go with the 60",
I have a 60" Moose on my 02 Foreman 450. and my Dad has a 48" on his Kawi, and after Plowing with the 60 vs the 48 it takes for ever to move snow around with the 48 inch blade.
Sublime out.
alot depend on your amount of snow fall your moving. I good up to about 8" of snow then the pushing gets tough. and If you due a lot of side walk's you might want to go smaller the 60 is to wide I have to angle it all teh way to keep the blade on the pavement and not rip into the grass.
but power wise the 450 can push the 60 blade just fine.