Been around a lot of Cubs mowing grass. Likewise, lowboys, 154's, 184's etc. Bottom line to me is a Cub for mowing is about the equivalent of a decent lawn mower from the 70's. By the '80's so many mowers began using higher powered engines that they would out-mow a Cub. Today it's not uncommon to see over 20hp hung on a 48" deck on a riding mower. A Cub with a 60" 3 blade deck is just not fast. However if you are not in a hurry, I think they are a good machine.
I liked the IH mower decks with the "overunning cutch" built into the pulley (was that just on the single blade 48" models?). It made shifting gears a lot easier. A more decent machine in my opinion is a Super A, 140 etc. You got enough hp there to get into some rather tall grass and still be able to handle it.
I guess part of my bias against using a Cub for mowing is that I never grew up with a tractor that small/underpowered. That said, dad has one he uses quite often. We completely rebuilt the engine and only mow lawns with it so it performs nicely.