"I'm looking to use it mostly for finish mowing. I also have a small motocross track that will be maintained with it. Any idea how much $ fwd would add? The local dealer has the 2wd for $9800. "
Reckon adding MFWD would cost about 2 grand..or less. But, that dual stage clutch is optional with the 2WD model and standard with the MFWD model.
Once you get the hang of it (short learning curve), the dual stage clutch is easy to use.
MFWD (Mechanical Front (or Four) Wheel Drive) is pretty handy, especially if you've a loader.
However, if you're not planning on a loader...I think I'd put the extra money the MFWD would cost you toward a hydro transmission.
Don't get me wrong..I'm strictly a gear guy! But, sounds like hydro would be a better way for you to go..if you're going to do as you posted.
The 790 is a mighty fine tractor. I really enjoy mine. But, for the tasks you described, MFWD wouldn't be particularly cost-effective.