Thanks for the inputs especially Shughes. I went to Hydro Gears site and looked up their specs. They rate each unit in max torque which is in Ft-lbs. but also lists the gross vehicle weight (GVW) for each unit used.
The EZT unit torque is 215 ft-lbs for a GVW of 900 lbs. My Hustler Sport is 500 lbs + driver 200 lbs = 200 lbs left to pull.
ZT 2800 unit torque is 300 ft-lbs and GVW is 1000 lbs. SCAG Freedom Z is 745 lbs + driver 200 lbs = 55 lbs let to pull.
ZT 3100 unit torque is 350 ft-lbs and GVW is 1200 lbs. Snapper Pro S50xt is 724 lbs + driver 200 lbs = 276 lbs left to pull.
I hope my examples and understanding is correct. I was surprised at the SCAG Freedom Z. Maybe that is why the SCAG dealer did not recommend any pulling. I have not calculated other mowers but I suspect that are similar.
By the way in my area, the Snapper Pro S50xt appears to meet my requirements ( 48" deck, Kawasaki engine, ZT3100 trans) and it was the least expensive of most of the mowers I looked at. Thanks Shughes.