I'm using a Frontier GM1072R (72 inch, rear discharge - it is made by Woods, equal to the 7200RD) rear finish mower behind a JD2520. I also have a 62D MMM for this machine, and I like the rear mower better. It delivers a better cut and is easier to get close to/under trees with. Only problem is that it is HEAVY (about 675 lbs) and is a little bit of a handful for the tractor.
I have very hilly, rough property with lots of trees, so it's hard to gauge the speed. Takes me about an hour per acre. The Frontier mower seems to be of excellent quality, except for the pain, which started peeling rather quickly.