I appreciate the feedback and I know of some of the issues you mention. My lawn is somewhat bumpy and that will make it so I cannot mow at full speed of a zero-turn. But I've actually used a zero-turn on my property (Deere Z930M) two years back for a full mow so I am familiar with the differences. During that demo, which was the first time I ever ran a zero-turn, I was able to cut my mowing time from 4.5 hours to about 3.5 hours. And that included my learning curve and taking time to bag several sections of my lawn (the Z930M had a bagger I had to connect in the midst of the session to try that out too). So I know for sure my mowing time will decrease notably. I'm fine shaving an hour off, doesn't have to be cut in half.Probably not what you wanna hear since it sounds like you’re pretty well set on a zero turn. IMO you will not shave two or maybe not even one hour off by going to a zero turn. The amount you do shave off will not be worth the amount of comfort you will be giving up. I’ve used both XMark and JD garden tractor X485 w/62” deck. The zero turn can mow fast but to do so much faster than your JD will result in you practically bouncing out of the seat. That, combined with having to constantly hold the sticks forward while cutting make for a pretty uncomfortable mowing experience. If you want to still enjoy mowing, stick with the comfortable seat, power steering and cruise control unit. Just my 2c worth. Good luck.
Plus, the zero-turn I buy will have some type of suspension. A seat at least, but possibly frame-based too like the Bad Boy. My x758 has nothing (except springs under the seat). So the zero-turn has to be an improvement. Also, my arms did OK with the demo I did so I'd expect that the more I use one the easier it gets. There are certainly a lot of people mowing with zero-turns so using the sticks can't be that awful.
Thanks,
Rob