Originally posted by Dunmer835 My main concerns with the Pentax K-3 is the autofocus
It's fantastic.
I never find it lacking.
Originally posted by Dunmer835 and that many of the lenses has no build in AF motor. I actually see that as both good and bad. One less thing to break in a lens.
Indeed, both good and bad.
Originally posted by Dunmer835 So I would like to ask is the K-3 auto focus up to par with the D7100
It's better in very low light, actually. The K-3's sensitivity goes down to -3 EV, other cameras go to -1 generally. A friend has a D7000 and is positively jealous. In bright light, AF is snappy and very reliable. You get 27 Af points, 25 of those being cross-type (the D7100 has 3) and 3 being f2.8 (the D7100 has one).
Where the D7100 is better is for tracking moving subjects. It works with the K-3 but Nikon's system is better.
Originally posted by Dunmer835 how bad is the noise from the AF motor?
depends on the lens. However, it has never bothered me. I have one "silent" lens and I o like it, but the others were never a problem.
If you don't mind giving up the Nikon stuff you already have, then from your questions I feel Pentax could suit your needs. Whatever your choice, it will be a big upgrade from your D80 that's for sure.