i like the idea of having a 48" stander and a 61" ztr. you could schedule the smaller yards on the same day if they are close enough to each other and just take the stander out and you could schedule the larger yards on another day and take the 61" out. or you could have a big trailer and carry both out every day. the choice is yours. the possibilities are endless. i have a 54" right now and a 21" pushmower. i use the 54" on everything. i only had one yard i used the 21" on. it was a fenced in backyard with a pool and took about 5 min to cut with the 21". that customer moved last year so right now i dont' have any use for the 21".
it all depends on where you live and the customers you have. some on here have alot of gated yards so a mower has to be 36" or less to fit through the gate. others have large open yards that are 3 acres and up and use bigger mowers.
my yards are about 1/4 acre all the way up to 4acres. i hope to get a 61" in the future such as the scag cheetah to add to my lineup. i do have a few yards where my 54" barely fits into places so a 61" only would never work for me.