I've lost track of which model has which preamps.
I compared the 60d directly with the 680 using the same mics on a piano, and they were very, very close, but I have no recollection about the preamps in the mkii versions. It could be determined by reading the various threads on each of these models. Seems like the pres in the 680mkii were mentioned in the 680mkii thread.
Of the 60d, 70d and 680, the 60d still has the best user interface, IMO. You aren't likely to engage phantom power accidentally and the 1/8 input is ganged. You also have manual control over the 1/8 output to camera.
The weakness of the 680mkii at the present price point is it's not that far away from the Zoom 8 with timecode. It remains to be seen what the Zoom will do, but I wouldn't sink $600 in a mkii at this point.
The 60d is virtually at a give away price in the YS lately.