I think Bet makes a more vigorous tree which with the Asians is a virtue in most situations but it is not considered reliably cold hardy for a Z5 so you are probably better off with OHXF. Maybe that's why the nursery sent it.

I found this in case anyone is interested. Bet. hardy to about -10, OHxFG hardy to about -20.

http://ag.arizona.edu/yavapai/publications/yavcobulletins/AsianPears.pdf

This article cites a book called Western Fruit, Berries and Nuts, published in 1981.

Dan

Fowlers nursery says not all bet is equal and claims to have an exceptionally hardy strain- or so a salesman told me many years ago.

If I was in Z5 I would protect it over winter with a mulch a few inches above the graft union.

I believe that I've often had it survive well under -10, but it was probably Fowler trees. Been a while since it's gotten that cold here.