I've had all three of the models. Lawn tractor manual shift, Garden tractor hydrostatic, and finally a Bad boy 60" ZTR on 3+ acres with over 40 trees and sometimes the right of way on the driveway that is another 2 acres X 3/10 mile long.ZTRs are specialized tools that do one job and do it very well. Garden tractors are utility tools that can be used for a lot of jobs, and do them effectively, but are not as good at any given task as an optimized, purpose-built tool.
I went from 8 hours on the tractor, to 6 on the hydrostatic to 1.8 on the hour meter of the Bad Boy. I also have a 72" finish mower behind the Mahindra 35HP but it takes about 3 hours and tears up the tree bark trying to cut close. ZTR for the win.