48'' walk behind faster than a 34'' ztr?

I'm thinking of getting into the commercial side of this business. Right now I have a gravely 34'' compact pro. It works good for my residential yards and gets into all my 36'' gates. It does do 9mph and cuts good at that speed, assuming the yard is not too bumpy. I'm thinking of getting a 48'' hydro walk behind to do larger properties. Would a 48'' walk behind be faster than my gravely? Or should I just use my gravely instead. I know the 48 is wider, but the gravely is also faster so I don't know.

48'' walk behind faster than a 34'' ztr?