In order to help you straighten and crop easily in photoshop elements which I noticed you have, take a look at this tutorial it seems the perfect solution for you (and me as I use PSE 11, upgraded from pse 8 ) link
I've always struggled with the organiser in pse 11, where it's awkward to zoom in to 100% and then return back to the same image in organiser, so often use picasa as the organiser and pse 11 as the editor, they work reasonably well together. However I found picasa can be a real pain with it's updates and corruption of databases etc so I refuse to rely on it and won't add any info to it because I've lost it too often.
As you can see a lot of people recommend LR, but invariably they always mention they also have an editor program because LR won't do it on it's own (even if it is very rare they use the editor). That always puts me off as I would like one program that does it all and not have to relearn how to use the editor every time I need it because it's been so long..... but LR keeps getting a good mention everywhere... maybe one day I'll add it...

I've been shooting with pentax for over 30 years and a couple of years back was tired of missing birds in flight shots, so I had a brief foray into Canon world to see if it was me or the Pentax. I can say from that it's definitely pentax, the Canon would nail shots I could only dream of with Pentax. Even with it's cheap consumer 55-250 lens it was amazing, plus metering seemed better for them also. I'm back with Pentax now, K-30 and it's an improvement but still struggles to match birds in flight with the Canon (30D). However it's still something I very much enjoy so I persevere with the following settings (which I've saved in one of the custom modes):
Turn off SR
Assign AF to the rear af button and disable from shutter release
Use TAv dependant on birds I'll vary shutter speed but for the quicker ones around 1/1600 is a good start
Metering tends to be multi with a bit of +ev dependant on lighting
AF-C, drive mode Hi
Single (centre) af point
Then get the bird in the viewfinder, half press the shutter release to start metering etc, but don't press the af button until the bird is over the centre spot, this stops the lens hunting and usually heads straight to the bird. If it does hunt or loose focus keep the af button pressed and move the camera until the out of focus bird is over the centre spot and it will usually lock on and then stop hunting. It's a lot easier if the background is sky it's much trickier if the background is trees etc.
This is the technique I use for my faster focusing lenses, i.e. the Pentax FA*300 4.5 and the Tamron 70-300 LD Di. However with my new Pentax 55-300WR the lens is so slow that if it starts to hunt I stop af, turn the focus ring to infinity and try again. Actually I also started to use manual focus a lot more with this lens and birds in flight, with the added bonus that the FPS gets a lot closer to 6FPS.
I do hope BIF's are not what you gave up Canon for though.

I use the following in this order
photozone.de
www.slrgear.com
www.lenstip.com
I think photozone has reviewed the Tamron, pentax 50-200 and 55-300 all in pentax mount, but you'll have to look in nikon or canon for the Sigma
Slrgear has the tamron in canon mount I think and pentax 50-200 (in pentax of course), can't recall about the sigma but hasn't reviewed the 55-300.
The other site is www.ephotozine.com but I find their reviews a bit varied as they seem to have many reviewers and little consistency on how they present the results.
Also the pentax only lenses have been reviewed at www.pentaxforums.com
Something to note is that other mount Tamrons have a micro motor for the af whereas in pentax mount it's direct driven from the camera and is a lot faster.
I'm not sure this will help with your indecision but it gives you something to read in those quiet non photography times...

Good? My opinion/summary.
The Tamron is the bargain with the fastest AF, with some of the sharpest pictures at the wide to mid end but can suffer from purple fringing at the 300 end depending on lens/lighting.
The Pentax DA50-200 is the smallest with reasonable AF and good images between 80-150.
The Pentax DA55-300 probably produces the best images at the telephoto end and is still ok at the wide and one of the best at mid telephoto, but is hampered by af speed.
I'd say if you go for the 55-300 and are interested in photographing moving targets go for the DA version (not the DA-L version) because it has quickshift manual override and that helps compensate for the slower than normal AF.
Now this is all just based on my experience of a limited number of lenses used in the field (K100D/GX10/K-r/K-30) rather than on a testbed.

I had the APO macro version of this lens for use on my film cameras, it came with a sigma +1.6 achromatic diopter that screwed into the front of the lens to give approx 1:1 macro. Trouble is it didn't play well on my digital cameras as it was the version before the dg coating. So I tried the Pentax DA 50-200 which jessops were doing at the time for £50 new (old jessops a long time ago). It's an ok lens but I didn't like it at the 50 or 200 end and used it in the 70-150 range. These days it just sits in my cupboard gathering dust. I added the Tamron 70-300 LD Di macro for approx £100 new (now about £90 new), and used that lens happily for a few years, it has reasonably quick af, 1:2 macro feature that works between 180-300 (although only 1:2 at 300), sharp upto 200 and acceptable after that to 300 at F/8. I've owned 2 copies of this lens and one was softer at the long end and had more purple fringing so there are some variances. However if you want a cheap telephoto option I think you can't beat this.
I now have the Pentax DA55-300 WR, which is slow at af compared to the tamron but holds the contrast better at the telephoto end although it doesn't look any sharper. So I tend to use this even though it looses in close focus compared to the tamron just because it means I have to do less post processing to get the final image. I'm not overly happy with the pentax lens either because of the slow and noisy af considering it's cost premium over the tamron, so I also end up carrying my Pentax FA*300 f/4.5 more often these days in preference to any of the above, but that is more expensive than all the above and less flexible.... I guess I'm trying to say in a roundabout way that at the moment I don't think there is the perfect xx-300 budget lens in pentax fit so compromise is the name of the game for me.

A lovely shot with good lighting considering how awkward these can be.
About the extension tube with AF, are you aware that that srb (http://www.srb-photographic.co.uk/pentax-k-auto-extension-tube-5913-p.asp) are now importing a K mount extension tube that is supposed to do AF as well? When I emailed them about stacking the tubes they said they have a 30 day return for refund or exchange policy. I was thinking about trying these although not on such lenses as yours, but have had to put things on hold for now. There could well be af issues though on a f/5.6 lens that you seemed to imply struggled with af in poorer lighting. Just a thought...

As I mentioned earlier I went out to a local wood, lots of butterflies with sightings/photo's of Silver washed fritillary, marbled whites, white admiral (no photo) and to top it off a purple emperor (distant photo in top of tree!) among the many others. It was a great afternoon.

Things do go a bit quiet at times, like you I saw a lot in spring, but I've just got back from a few days in the north east (England) and I started seeing ringlets, meadow browns, large skippers, fresh small tortoiseshell, speckled woods plus the occasional red admiral and peacock. Don't worry I think they're coming..... Thought I'd go out to a local wood later today (southern England) and see what's on the wing. Who knows maybe the purple emperor will be around (there have been sightings down here already) along with white admirals and even some black hairstreaks... Oh how I love summer....

Thanks for the details, sounds like you work as I do adding/subtracting ev as required, only you're much better at it than me! Also sounds like you are fighting the same issues trying to get the af to lock on when the background is not sky. A couple of weeks ago I was out taking manual focus shots of hobbies in flight (because the af issue) and walking back to the car a barn owl skimmed by, I now have out of focus AND over exposed shots of it.... Just got to keep trying.... Thanks again for posting.

Lovely captures. Any details on camera, lens and af settings? (plus exposure settings for the one against the tree, I always blow these when following from sky to trees and just get too excited to remember to dial in ev compensation...)