Yeah I went to BMCC a month or so ago, and it’s well slippy in the wet! There wasn’t an awful lot of choice trail wise, and what was there was pretty hard to clear given the lack of grip, but it’s still worth a look, I’ll probably wait till the summer though before going back, it’ll be mega fast in the dry.
Having never done Cwmcarn, I’d chose FOD out of the ones suggested, yes it does get wet in places, but I’ve always enjoyed it there even in the middle of winter. Plus they have a cafe and bike wash.
Is Gawton within reach? Never been there myself, but it’s another option.