That's what I did.
First I analyzed all of the stabilized lens options available. My thought process was as follows: I figured I wanted a fairly wide range zoom lens--something along the lines of 18-70mm. The best zoom lens in that range (for a sane price) is Sigma's 17-70mm. K10d, D80, and Xti can all use that lens, but the K10d is the only one that provides stabilization. Canon users can buy Canon's
18-85mm stabilized lens (I'm going from memory on the FL), but according to reviews it's pretty poor IQ--much worse than the sigma. So the K10d was the only way, at the moment, to use that excellent Sigma optic while getting stabilization.
The other thing the D80 had going for it was the 18-200 VR which is the best of the three 18-200 available (Tamron and Sigma also make this range.) However, IMO, that advantage just went out the window with Tamron's new 18-250 which appears, to me, like it's going to at least match the Nikon optically while having more range. Again, the K10d is the only way to get that range stabilized.
People say the D80 focuses faster (although I've seen head to head comparisons in two reviews and in good light the K10d was faster in both comparisons. The D80 is faster in low light)
I've seen nearly universal agreement that Nikon's flash system is better, so that's another consideration. The D80 also has (again IMO) sharper jpeg processing, but from what I've seen the D80 noise reduction at ISO1600 is too heavy-handed and everything looks smeared out.
The K10d will overwhelm the D80 with creature comfort features--RAW button, Sv mode, TAv mode, better continuous modes, fancier bracketing, better UI, more focus points, et al.
I strongly recommend you handle both cameras in a store if possible. Handling is a big part of the DSLR experience I think, and you can't get that from a review.
Bart
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