After owning a Husqvarna Rider 155 for 9 years and 2,000 hours on it, I decided, after comparing bigger mowers, to stay with Husqvarna. We have LOTS of slopes on our 12+ acres, and certainly didn't want to spend $30K on a slope mower.
Furthermore, we didn't think that the the Rider 155 with the TorqTuff K46 transaxle was going to hold up to the strain of trying to climb hills forever. So - we went with the Husqvarna Garden Tractor GTH26V52LS, which is a 26 hp Kawaski engine, 52" cut, and Hydrogrear transaxles.
The powerful 26 hp, tri-blade welded deck mower just doesn't care how tall the weeds are - it just blows right on through them. As far as the 25 degree slopes, we had a traction problem, even though it is a "posi-trak" type transaxle. So we added 2 - 50 lb. wheel weights. That made the mower more stable on all terrain including the slopes, and traction is not an issue at all.
This mower is not for "lawns" - it's for "yards". We're still using the articulating Rider 155 for very close work, and small areas that we want to look super-nice. The GTH26V52LS is not as smooth cut as the Rider 155 or many other lawn mowers, but it does a 'good' job of cutting. And, it covers a lot of any type territory that you probably have, very quickly.