Fountain42,
I have a BB2060 for my 2520. I use it to do a lot of tasks. When scarifying or moving a lot of dirt, the tractor can reach a culminating point where the differential lock may or may not make the difference. You'll want to purchase a 60in instead of a 72in.
You may have a task in mind, right now, for your BB. A BB has an infinite number of uses that you can search for on this site, and those uses may not be in your mind right now---- but you will limit your own future capabilities if you buy "too big". Go w/ the 60in.
v/r mark