Yes, a 54" mower will do the job done pretty quick. Even a 48" ZTR will do the job just fine. A decent 42" ZTR would work but it would take longer. A 60" ZTR would cost more and might be overkill for your needs/budget.
A 48" ZTR will cost less than the 54" for a couple of reasons (assuming the same grade of mower). Main reason will be engine size necessary to power the unit.
And Larry has a good point. A rider/tractor will also do the same job (just not a quick but at a lower cost).