Canon 40D vs. 50D

I would be interested in any opinions as to which is a better DSLR for AstroPhotography, the Canon 40D or the 50D. In comparing the two cameras, the specs are virtually identical, except as to number of pixels and pixel size (pitch). From what I have read, a larger pixel is better, all other things being equal. The 40D has pixels that are about 20% larger, but it has 10.0 MP vs. 15.1 MP for the 50D. Also, the 50D tends to run about $200+ more. If the 40D is better -- case closed. But if the 50D is better, is it $200 better?