You can stay in the PL set till 61, just add some B-grade common parts into your PL set (Gloves, Circlet/Helmet) and you will be fine.
It can save you some money for A-grade. When I was in B-grade, I was using Avadon as an indifferent set, just because it was the cheapest one I could get. But nowadays I would deffinitelly stay in the PL - its cheap like hell.