You wouldn't believe what I have gone through to get a smooth ride on a lawn mower. Between drought cracks in the rock hard clay and hoof marks, it is unbearable with the suspension systems normally sold. But after tweaking springs, a suspension seat, an air shock system I built, knee action front axles, an air cushion like OTR truckers use, and running the tire pressure as low as I can (10psig or less) I finally got something that works.
On mowing 30 degree pond banks I posted somewhere else here on a forum, I have a conventional mower for that and explained how it's setup. Took long enough for me to get it right. Main problems were center of gravity, traction, and weight of the machine. My ZTs just couldn't hack it.
On lumbars, the OEM machines you buy with the regular suspension having lumbar molded into the back of the seat, drive me nuts as your bouncing up and down just rubs your back raw. With a floating suspension and reasonably smooth terrain, I'm sure it's a different story as you said.
Mark