Sorry if it sounds a bit negative, but this whole crop factor thing is very meaningless unless you are comparing on the same pixel level.
For example, I have a 30D and a 5D Mark II, the 30 is a 1.6x crop factor and the 5DII a full frame. However, the 30D is 8MP and the 5DII is 21MP. The number of pixels that hits my target if I put the same 500mm lens on both camera is exactly the same. The pixels at both 8 microns which means I gain no extra resolution, however, I get the extra viewfinder range with the 5DII, and I like that
Just make sure you don't fall in the same trap as everyone else. You aren't getting 800mm reach, you are getting 800mm field of view on a 500mm lens, which means you are more or less losing out. However, if my 30D was 16MP, then I would get double the pixels on my subject, increased resolution, and potentially a better, larger file.
Lesson: compare pixel sizes in the sensor, not crop factors if you want to make an educated decision.