Best answer is check out the guys that work for the state, like the Texas Department of Transportation (DOT). These contract guys go through **** trying to mow highway right of ways and do one heck of a nice job. The 30+ degree banks they mow are the real "how do they do it" for me.
Most use JD cab, 4wd, don't know if hydro or not. Mower I recall is Mohawk and JD. I think the biggest thing in that kind of mowing is if you could get a seat like I have seen in some combines used in wheat country where the whole thing tilts to level while the chassis follows the terrain.