I have neighbors on all sides with ZT mowers, with one having a tractor and ZT. He does the bulk of the yard with the tractor and goes around the house with the ZT. All of the neighbors with the ZTs mow at roughly tractor mid-range speeds or slower, and get done in similar or slower times than I do on my LS with 72” cutter at mid speed. The pro mower who does the front property (about half the size of mine) takes several hours on a ZT, because he goes maybe 4-5 mph to get a good cut while avoiding hitting the uneven spots at high speed. The big tires on my tractor don’t care about those spots in my field, so I get done much faster. We all have the same basic landscape, as it was a giant property that was cut up and sold at some point in the past.
Come to think of it, I don’t know if I’ve ever seen anyone run a ZT at 10+ mph anywhere. It may be possible on a soccer field or a golf course, or someone’s HOA neighborhood with perfect yards, but it’s just not something that seems to be done on a pasture, field, highway median, school grounds, or anywhere else you have less than perfect conditions. At least in my observation.
Now I will concede that a small SCUT is probably not going to perform anywhere near ZT efficiency, even with a 60” deck. I had a little BX for a while, and it just won’t compete. However, I get to cut in the AC in the Florida summers on my cabbed LS, while all of my neighbors suffer! (I know, I know…not funny. But it really is worth having AC and sun protection when it’s in the high 90s with close to 90% humidity.)