Looks like you have a real utility tractor for heavy work, so if you're only basically mowing and maybe towing a light cart, IMO the convenience of the hydro when mowing would outweigh the longevity issues, if any.
I've got a hydrostatic drive Toro 417 that weighs 657 lbs without the 48" deck, which is probably another 200+ lbs. We me on it, it weighs over 1,000 lbs. I've moved a trailer weighing around 2,000 lbs without any problem. It's got enough power to be rated to run a 36" rototiller. It's got only a 17 hp Kawasaki twin and power does not seem to be an issue, so the 20 HP on the Craftsman should be adequate.
I really love the convenience of the infinite mowing speeds the hydro provides. I'm not confined to just 5 or 6 set speeds of a manual transmission. Keeping in mind that 5 and 6 and maybe even 4 would be too fast to mow in some circumstances, you're limited to 3 mowing speeds with a manual.
I like the manual in my JD 770, but am glad I've gotten the hydo for not only ease of operation but the ability to run at exactly the mowing speed I want.