I, like the OP, never considered Pennzoil until I stumbled upon BITOG. Of course, at that time I was drinking the RP kool-aid. I would not hesitate to run Shell products now (I do, in fact, run it in all my OPE).
While certain flavors of Castrol don't have amazing specs, many of their products are also well respected here at BITOG (0w-30, 0w-40). They just have some weak links in their product line.
Welcome!