I can just see that at the next Asian wedding he tries to shoot. (Maybe he can commandeer a desert trolley?)

Wow... are you kidding?! I'd say build-wise, the 50D probably feels ever so slightly tougher than the K5, albeit it isn't so well sealed.

I rush too much too. I feel a bit sensitive about annoying my subjects or (in other countries) making them feel like 'tourist exhibits' so frequently walk away knowing I could have done better. But it's the thought of doing it better next time that keeps me coming back to photography!

Another advantage of a prime, though, is it does buy you a little more time. It feels less intrusive somehow, than a stonking great zoom. I am tending to stick a prime on and then seek opportunities for shooting with that lens, and simply accept that some opportunities will be lost. I find the better quality and 'character' of the prime lens shots does tend to make up for the losses.

I really like the first and second shots, and the three boys shot is great!

The low light shots look a bit on the murky / orange side.

As a general note, which applies particularly to the shot of the old lady in the market, the three boys [Edit- girls!], and the girl with the SUV in the background, I would like to see much narrower DOF than we see here.

The 50mm would have allowed you to isolate your subject much better though, at f2-f4 apertures. This is something lacking in the old lady shot, and the shot of the boys [Edit- girls!], where the background and surroundings distract and reduce the shot's potential impact.

Of course including a subject's surrounding context is important, I'm just saying it doesn't all have to be so sharp it fights for attention! More like the background in shot 2, which I like!

A nice set indeed though.

Doubtful. Although Mark's advice is very good.

Both images were taken under exact same conditions (same tripod, same 6 sec exposure), and confirm the OP's general observation that his K5 images are soft.

The only thing that may have caused more softness in the Pentax is the SR, which I have already brought up. This needs to be turned off. But I don't think this is the cause of this amount of blur, especially when the softness is borne out by the OP's observations under normal conditions.

You said that it isn't possible to manual focus at wide apertures... K was just saying that it is possible, although easier with a split screen.

For me, I find it very hard to MF using the standard focussing screen. I resort to LV or my patented 'somewhere in the middle' technique. (I slowly and smoothly move my focus so I see the object come into focus and then go out of focus... then move the focus back again, and again see the object come into and then go out of focus... on the third pass, using 'muscle memory' I click the shutter somewhere between the two points!)

It sometimes works!

Yep and jpeg would make more sense for these sort of 'testing' shots as it's quicker to deal with.

I wouldn't get hung up on that. Your concern is the gross lack of sharpness, not minor differences in tone and colour. You can twiddle about with the Pentax files to make them look just like the Canon files and vice versa but this is beside the point really. (After setting up the presets, it's over to you to make adjustments according to your own taste and your intentions for the image)

The Canon looks OK to me, considering it's the kit lens. Nothing a quick sharpen in PP wouldn't fix! When your Pentax set up is working properly, the same will be true.

Well... we can see the photos and we can see something is wrong. That's a conclusion we can draw without reference to test charts etc...

I presume you've turned SR off for the long exposure?

The first image is OOF but seems less so in the left hand corner, perhaps.

The wall there is closer than the ear area, so perhaps the lens is front focusing? Try again using AF in live view. If results are better, you know the lens is front or back focussing wildly. If not, it's something else....

This will not be the 'FF in tungsten light issue' IMO, and more likely a front or back focusing kit lens. Or it may be that the lens has been doinked in transit and needs replacing by Mr. SRS. To be sure, try a different lens!

I really, really doubt this has anything to do with the camera body itself, in either case.