I own 60D and 5Dc, previously owned a 7D. I don't shoot birds or wild life, so most of my pictures don't require heavy cropping, my observation is based on this apparently.
I noticed that when looking at mRaw from 7D/60D and Raw from 5Dc, at 100% crop, 5Dc seems to have better center sharpness in most cases. I'm not saying that it can't be sharp from 7D/60D, but if I shoot the same lens on both bodies, say tamron 28-75, in general 5D pictures look sharper than 7D/60D.
Is this because of higher pixel density on crop ? Even at 10mp on crop vs 12mp on FF, the actual density on crop is still about twice of that on FF?
I did notice that lenses with weak corner sharpness seem to be better on crop than FF, say my 20mm 1.8, which is terribly soft at corner wide open, it doesn't look that bad on crop.