Well, from what you're saying there, it comes down to length doesn't it? If the 135mm reach is enough for you in lower light (and obviously you have the prime so probably have some idea) then get the pentax 50-135.
If you think you need to go out to 200mm get the Tamron.
They're both very well regarded lenses, you can't really go wrong with either. Obviously with the pentax you get the benefit of silent focusing and weather sealing, as well as it being a little lighter.

In the end I personally decided to get the sigma 70-200 HSM. I wanted the reach out to 200mm, but I also wanted the silent focus.

Yeah, sounds plausible. Might be worth investigating whether a Sigma camera with a Foveon sensor mitigates the problem (not a very cheap solution!)

I suppose the best bet might be to try and negotiate with lighting techies to get 'flatter' light for your shoots? I'm presuming working in theatres you aren't usually working during actual performances?

It'd certainly be a neat trick, and a useful thing to have- I can't see any reason why it wouldn't work.

I suppose the risk with this sort of feature however, is someone trying to do it hand held and making an absolute mess of their settings, rather than doing it in a controlled environment on a tripod.

Yeah, you already told me that one... lucky I was sitting down!
Fortunately, I got my 360 flash in a John Lewis clearance for £90, so I can happily tell you to go swivel with your fancy flashes!

Aw, c'mon, it'd only cost you £400 to replace it if the other one got lonely...

Hmm. From what you've said Chris, I would:
Sell either DA 18-135 or FA 28-200. They're pretty similar in range, and it doesn't sound like you're wild about either of them.

If you're selling the DA 18-135, you probably only need to sell one 400mm. If you decide to sell the FA, you probably want to sell both of them. They're both hefty, and I just can't see you wanting to use either in preference to the flexibility of the Bigma.

Keep the DA55-300. Consider it the Littlema replacement for the Bigma when travelling light.

It sounds like you've already decided to sell the a28mm - if you never use it, sell it. If you need something in a similar range down the line, get the DA 35mm f2.4. It's lighter, brighter and auto focuses.

If you still need more money after those, sell me one of those flashes for cheap

Hmm. In which case Chris, to be entirely honest I'd be thinking about a trip to SRS to exchange it- I know you got it fairly recently? It sounds to me like the battery life you're experiencing is considerably worse than I've had on my K-R, and is certainly well below where it ought be for the K-5.

If it's too late to exchange, and it's a question of waiting for a repair, then I'd probably just buy a couple of spare batteries and make sure I always had one to hand, as I wouldn't want to be without my camera!

The only thought I had, and forgive me if this is a stupid question, but how have you assessed that the batteries are flat?

Are they so flat that the camera won't turn on anymore, or is it that the battery indicator is showing empty? If it is the latter, I'd suggest that you try fully draining the battery somehow (eg taking a long video, then repeatedly turning on live view when the camera is showing low battery, focusing a lot, mucking about with powerzoom if you have such a lens etc) until such a point as the camera won't switch on anymore. I'd recommend you do this with no memory card in, or at least a memory card with nothing important on.

Once you've done that, you might find that the next full charge will last longer. That tends to be the way it goes with my phone, anyway!

Well to save the battery, when not in live view, it only actually moves the sensor (performs shake reduction) during the actual exposure- there's nothing to be gained from moving a sensor that isn't in use.
When in live view you get the benefit of a stabilised view, so it is on all the time.

You're hearing the shake reduction. If you turn off sr, the noise will go away (and your view will be more shakey.)