I actually like the loader on for stability and I am already mowing as fast as I deem safe.Have you tried mowing those slopes with the loader off? I can pop the loader on and off my B2601 pretty quick and gives me a good bit more power. Problem with the B2601 and the loader off is the front end becomes very light. Have to be careful.
I would think an L3301 or L3901 with spacers and filled tires with the loader off could lift a 5' or 6' finish mower without having such a "tipsy" front end and have a good bit more power to pull up the slopes.
Dan