RON ARMBRUSTER - DO NOT put any faith in anything Brian Miller says on his website!
If your interested in garden tractor pulling look at MIDWEST SUPERCUB's website. read their question/answer forum. Most all pulling tractors regardless of what color they're painted and what brand sheetmetal they wear are CUB CADET gear drives where it counts.
I try to stay away from the gear drive vs hydro debates. I have the #70 Dad traded an Original for in 1965, but it has a 10 hp Kohler in it now. And my #72 I bought in about 1979 or '80 has a 14 hp Kohler in it now. And I have a 982 with 20 hp Onan and all the options, 3 pt hitch, frt remotes, rear pto, and steering brakes, and hydro transmission. For heavy draft jobs, moldboard plowing, grading, etc a gear drive rules, first and reverse, or 2nd and reverse. I was at Plow Day #2 when the ground was packed hard and turning over in huge slabs, I plowed in 1st gear all day. The hydro's plowed faster than me but they had to stop and cool their hydro oil every round. In normal plowing conditions you don't have to stop with a hydro. I never had to stop at all except for gasoline.
Depending on what your going to do with your Cubbie, follow Scott's advice, buy the highest HP hydro you can find and afford. a 14 or 16 hp or higher HP 2-cylinder engine. It really doesn't cost any more to run a 14 or 16 hp engine than it does to run a 10 or 12 hp engine, but the bigger engine lasts much longer.