Good tires are very important. I like the chevron tread tires becasue they give good traction and don't tear up the yard. My yard is much steeper than yours. 20Hp should be plenty of power (unless you are an unusally large person) to climb the hill. (I have a 22Hp.) Getting enough traction is my biggest problem. Do to the layout I can't get a run for the hill, so if the grass is damp I won't make it up. Adding weight to rear wheels has helped some. With a 20% inlcine you should no problem with either tractor. Hope this helps.

Hi Dave,
My place is 13 acres some of which is very steep. I have a Craftsman 5000 and immediately put the chevron tires on it. I reccommend as much horsepower as you can afford since you may find mowing is only one of many things you will use it for. I use mine for dragging brush up out of my ravines, maintaining 1/4 mile of gravel road, plowing about 4 steep acres to avert fire hazard. Be careful however my may well become an attachment addict. My latest is Craftsman's pull behind log splitter. With the chevron tires, I can pull as much oak wood as my trailer will hold plus the 220 pounds of me up pretty steep hills covered with leaves.
Mac of the Sierra's

Just a word of caution. I met an old man recently. He had been mowing "down by the river" when he flipped his tractor. The mower blades got his left foot, tore it up pretty good. He crawled for help, was airlifted to a local hospital. They amputated his foot, got sepsis twice, got 2 more amputations and ended up losing his leg above the knee. When I met him he was waiting for surgery to replace his other knee's artificial joint. He sure gave me pause. But for the grace of god...