Interesting, I haven't read through all the replies yet, but looking at the 1st page, the picture of the girl in white dress seems back focus by quite a bit, I used to use K-5/K-5IIs and Tamron 70-200 quite a bit and I would say auto focus system in the original K-5 was really letting the side down, I've got a lot more satisfying result after I finally got fed up and bought a K-5IIs to replace it. I actually shot my friend's wedding and his daughter's christening in very dimly lit church with the same combo using much much higher ISO like 3200 and still got acceptable results.
I'll provide you with some example of K-5IIs and Tamron 70-200 at similar settings
200MM, f4. ISO800, 1/250th
200MM, f4.5. ISO800, 1/200th
87MM, f4.5, ISO3200, 1/80th
For portrait and stuff, flash would help tremendously, in the end, photography is all about the light. learn to use (manual) bounce flash(P-TTL for bounce is just not reliable) and off camera flash and you will find your shots improve dramatically. Check out online resource like strobist.com on flickr (
http://strobist.blogspot.com.au/)and youtube(I quite like Zack Arias' old one light tutorial but I think they have all but disappeared from the internet), it really helps