the "gt" series is about the bottom end for a j.d. machine built to last.
for 2 acres, the 200 series is minmal. i think a man that keeps his machine 10 or more years would be better off with the 300 series.
for 2 acres, no less than a 48" deck and 16-18 h.p..
for a 3/4 acre yard, a 38" deck will get you by, but it still takes h.p. to spin those blades fast enough thru the heavy grass to keep travelling at a good clip.
hydro is fine if you do lots of stopping, turning or have lots of crap (shrubs, trees, landscaping, decorations) to mow around. for wide open spaces and long runs, i prefer my gear drives. for hilly terrain, i prefer gear drives. for working the machine for anything other than mowing (cultivating, rototilling, plowing, pulling other things around), i prefer gear drives.
one of the best things about john deere is the parts support. all machines break and wear out. i know of no brand that comes close to j.d. for spare parts support. some of my machines are 25+ years old and i can still have parts shipped to my door with j.d.'s 24-hour parts support network. if they go down, they aren't down long.