If you're cropping to the same number of pixels with the K3 compared with the K5, you're obviously not going to get the MTF benefit I mentioned, in fact that will be more demanding of lenses - probably still better than using a teleconverter to get the same effect though (and you get more control over the framing in post! As to AF tracking, I haven't had much opportunity to try that yet. I believe someone (Atavar?) gave some useful comments a few weeks ago about how the K3 compared with a high end Nikon - I think his conclusion was that while the K3 has Pentax's best ever tracking AF, it's not quite up to the best Nikon can do - which is about what I'd expect. Other reports I've seen suggest that tracking AF performance of the K3 depends quite a lot on which lens you use. See, for example, DPreview's comments here: http://www.dpreview.com/reviews/pentax-k-3/8 So this all probably muddies the waters for you rather than clarifying your decision - as I understand more about what you want to do, it's clearly different to my own requirements (mostly landscapes, occasional wildlife when it shows up), so your benefits from the K3 aren't as clear cut as mine. However, my overall gut feeling, FWIW, is that the K3 will give not quite as good performance for what you want as the D810, but for rather less money, and should be better than the K5. Exactly how much better is hard to say, but it should give you a lot more options, e.g. cropping.