Love my 40D, have used the hell out of it since 2007. I would possibly say the step from 350D to 40D was more significant than the step from 40D to 5D2 (which I only made last week after canceling pre-orders on the "3" and D800).
One of these is a 40D. One is a 5D2. Both are the EF50mm f/1.4. Without pixel peeping (or EXIF cheating), I would be hard pressed to tell which was which.
I would say the first is the 5DII
Would be interested to know how you got more bg grain with the 5D2 then - bigger crop, higher iso??
Substantially higher. 40D @ 100ISO, 5D2 @ 1600. Both at f/2.5. 1600 wasn't necessary, though, just playing with the camera. 5D2 was 1/500; I generally aim for 1/125-1/250 when shooting my boy, and not so wide that the tip of his nose goes OOF.
Again I was picking a 5D2 image to try and match DOF to eliminate it as a giveaway. Something like this makes it more obvious (400ISO, f/2.8 )
Also, I'm driving the 5D2 the same way I drive the 40D (manual exp, generally half a stop left of center in the exposure meter - don't want to deal with ETTR). Perhaps with time I'll pick up a better way to get more out of the 5D2. Either way, I think that the 40D is still a viable camera. It has its weaknesses (ISO gets silly in a hurry), but can deliver.