You have gotten some good comments on the Ford, JD's and IH's. If you are not too much against a MF again you might look at the 383's and 393 tractors. Nicer(and more complicated) are the 4200 series, in which the 4243(I own one of them

) and the 4253, but you would be looking at quite a bit more money than the 6610 or 7710 tractors. The 300 series all had a good reputation and many are around that are still good solid tractors. I just don't see many with MFWD around though. A lot of the newer 400 series(471, 481 and 496) would fall into your size rating and many have MFWD, but again you would be taking a step up in price(but maybe not as much as one would think). All mentioned have the proven Perkins diesel engines in them.
My neighbor has a 6610 with a cab, MFWD, and a loader on it. I can say that it has never been babied and abused might be closer to the truth. The A/C is a regular problem on his. His main maintence issues are mainly age related hydraulic leaks and his is a bit of a hard starter and isn't making full power due to(most likely) clogged injectors. It has been that way for 3 years that I know of.

When he bought it several years ago it had somewhere over 5000 hrs and he used it to bale and batwing with. I have run it and shifting is actually pretty good. Much better than a lot of the old IH's I have run and much, much better than the old Ford 9600

that I owned.
With all that said, I would have to say they are tough tractors and if you can find one in better shape than his they can be a good buy.
As an opinion for someone who has had both tractors with duals and MFWD. MFWD is better for anything with a loader on it, especially in wet weather and the larger front tires make for a smoother ride otherwise. Duals are great for high traction needs in fieldwork, not very good using a tractor to brushhog with and can be a real pain (IMO) to take on and off.