I have a Rebel XTi (400D) and am thinking of upgrading. I'm not interested in spending the money for a 5D so that's out. Is the 30D really an upgrade (8.2mp vs 10.1mp). I know the build quality is better but will the images be any better? How about some of the older models like the 10D or older 1D. How important are megapixels when it comes to image quality?