Walking a fine line, here, Bill.
The following is an opinion - and we know what they're worth.
It sounds like you've kind of ruled out the higher horsepowers, which is not a bad thing because I really think that a properly running 10hp will run quieter, smoother, and do about anything the higher HP's will do.
Sounds like you're wanting to build a show tractor?
I came to the conclusion years ago that sentiment is expensive. You neglected to tell us what your sentimental Cub Cadet is.
My downfall was a 105 about 15 years ago, which was also my introduction into sticking hydro relief valves and "Hey, these have to be split just like REAL TRACTORS." That particular 105 got to be running, moving, mowing, sold to a friend that wanted a woods tractor, stripped down, engine changed (went from Smokey to Ollie (Oliver) -- the sentiment doesn't stop. A month ago he told me that since his situation has taken a drastic turn that if Ollie changes hands he'll come right back here.
My opinion - 10HP. Hydrostatic? 105 And this isn't a for sale post 'cause I ain't got one!