Renting for the weekend is a great idea. When I tried the D700 in the store it felt great...But you really need to shoot with it for a few hours/days to see if your body agrees with with the initial feel.

and that's so true casil about the big box stores and cameras. The salespeople know very very little about the cameras. If I wanted the information written on the side of the box, I'll read it myself.... that plus I find in general the WORST camera deals are at the big box stores.