gw . . . I don't know anything about the SX series tractors and didn't see them when I looked on the Deere website. Maybe I just didn't look in the right spots.
But I have a Cub Cadet with 75# wheel weights and snow chains that I used to mow my lawn, which has several steep hills. If not for the chains, the tractor would not make it up the hills in the middle of the summer.
I still use the Cub, but now it is at my office on flat land. I switched to a 4wd lawn tractor (Ventrac) that has turf tires and it just climbs up the hills with absolutely zero slippage. The difference between 2 wheel drive and 4 wheel drive simply cannot be compared. If you want to put bar tires on a 2 wheel drive tractor and climb steep hills, I think you will end up spinning the turf off your steep spots leaving you with bare dirt. I have that in several places on my property and this year I'll be putting in sod on those spots now that I see that the 4wd mowing tractor doesn't spin its tires at all.
You MIGHT be fine with the 2 wheel drive tractor if you add weight to it and if you add bar tires. But I think it is very safe to say you WILL be fine with a 4 wheel drive tractor. I tend to agree with what Fred posted above, and as he has a 335 that seems to me to be reason enough to doubt the 335 on your property.
The problem we all have when we give advice is we don't know what one person means when they say hills versus what another person says. In the long run, I think you will find that you might want to error toward a 4wd than a 2wd, even if it means finding a slightly used unit so you can stay within budget.