My speed while mowing is determined by the smoothness of the ground, the number of obstacles that I have to go around, and most importantly, the sharpness of my blades. I have never mowed with my zero turn at full speed. I have mowed with it at such a slow speed that I'm barely moving forward. I'm not in a rush to finish, I like to have a nice looking lawn when I'm done. I had asked my son in law to mow one time and he did such a horrible job that I never asked again, and ended up mowing it right after he left. His mom wanted me to include him in doing stuff, but that was a bad idea. I also have Bahia grass, and the stalks are very abrasive on a mower blade. The only other type of mower that could do my yard and area around my house would be a push mower. I had a Craftsman riding mower before the zero turn and there where areas that I just couldn't get to, or out of, so I did a lot of weed eating. A tractor just isn't an option around the house.
Out on the land, mowing my walking trails with the zero turn is also at a moderate speed. It's not as smooth as around the house, but it's more fun because I'm out on the land and wondering through the woods and along the edge of my pastures and across the top of my dam. It's really kind of fun mowing those areas. I go over those trails twice. All the way in one direction, then turn around and mow it wider in the other direction. 60 inch deck and I'm maintaining at least 9 feet wide of well mowed, easy to see snakes, type of walking trails. My guess is that it's a mile and half each way.