In three consecutive years, we pulled the same wide conventional-tillage drill with a 7520 Deere (the old articulated 4wd) then a 7120 MFWD and then a C75C Challenger.  I would say the endrows were roughest by far behind the 7120, then the Challenger, and smoothest behind the 7520.  The Challenger has 35" belts, which helps it a lot compared to anything narrower with centered guideblocks, and the 7520 could have been even better if it had wide tires instead of the 18.4s it had.  I really don't think there was much hope of getting the mfwd to do a nice job...weight distribution is just tooo messed up with 40% on the itty-bitty front tires which are already being pushed around the corner....they'd be making ruts if they had an appropriate amount of weight, it's hopelss when they have to be aired up to 30psi to carry the overload built onto them.

wheaties is exactly right regarding the belts....put an idiot or someone who is determined to make them look bad on the tractor and you'll get a mess.  Put a decent operator who gives a damn in the seat and they can be run very well.