I've had the 60d and currently shoot a 5d and 50d. I didn't really like the files the 60d, or the 50d for that matter, produces. It's not something I can quantify, but I assume it has to do with pixel density.
Although the 5d and 60d are pretty similar in high iso performance, with the 60d having a higher native iso, the noise from the 5d is, IMO, nicer. It has more of a film grain look to it.
So far for me, the 5d and 1dmkii have been my favorite cameras from a pure image standpoint. The 5d is a bit awkward to use, but I simply love shooting with it. Even when my 5diii finally comes in, I will keep using the 5d; and to me that says alot.