Gregfender,
When you say 70% hilly, can you describe any further? Do you mow all the hilly area? How steep are these hills (what angle if you have a angle gauge?)? Do you travel along/across the side of this area or do you go straight up and down.
I have a DK40, R4's, loaded. I'm on flat land. I've had no issues in the snow so far, & that's in and out of some mild ditches too. I did manage to bury my front end up to the axle this summer but that was b/c I ran right over top of the area I had used a subsoiler on and didn't see it b/c of the tall grass/weeds I was mowing at the time. Put it in 4x4 and backed out....that's my only experience w/ getting stuck.
The other reason I ask, is that I had the opportunity to mow w/ an Uncle's Kubota MX6800 cab w/ a 10ft brush hog in Kentucky. His land is anywhere from a 5 degree to around 45+ degree angle and he has R1's but they are doubled up on the fronts and rears for running around these hills (not just going up and down). He even has a 3rd set for it but wasn't using them. I got to mow a large section of it and that was test of nerves for sure!!!
Your center of gravity will be a very important issue where your hillside activities are concerned. Keep that in mind.
Good luck!