72" mowers cost a lot more than 60". Yes, it is overkill most of the time.
Actually, a 52-54 would be better for me because it get's in a lot more places. That's why I have my WB.
You'd be surprised how much a 60 will get done.
One more thing, a 60 probably would be easier to sell in the future. Not to say the 72 wouldn't sell but there would be more people interested in a 60.
Most landscapers that own 72"s already have their bases covered with 60"s and just need a wider mower, usually for some extraordinary big open areas.
If you get a 72, get the biggest engine available. BTW-My 60 has a 25 Kawasaki and it performs great.
Remembering all my departed friends.