If you're doing portrait, landscapes and close-ups I think most situations should be fine and not so challenging, light permitting.
For sports and birding, I've used slow lenses like my Pentax 100-300/4.7-5.8 or Sigma 170-500.
The centre point always works best for faster moving subjects and I can switch to another point if the subject is moving slower.
I think that's down to me and my technique or lack of it. I lost a few shots on some of the outer focus points.
My tracking technique still isn't the best and have also tried switching to manual mode.
In lower light it's necessary to pump the ISO up as much as possible to affors a faster shutter speed with the lenses above.
I'd say the K-5 can give good results at ISO 6400.
Have you considered using a tripod and manually focusing for you photos?
I recommend it for the landscapes.
This thread might be worth checking out:
https://www.pentaxforums.com/forums/pentax-k-5/177437-auto-focus-s-vs-auto-fo...servation.html