1D.1 is supposed to be the best, however I've never had problems with 1D.4 or 2B motherboard revisions + Mediator, PPC, Grex, or any other heavy-duty A1200 expansion.
I think that those timing problems are rare, or perhaps Blizzard cards (which I mostly used for testing) are handling different mobo revisions better than other accelerator cards (e.g. Apollo).
