I did wonder about the 'two manufacturers' thing. Maybe the BIOS is designed for either of the two.
I've tried the beta blockchain drivers (with DDU between attempts) and the newest drivers, with multiple uninstall/reinstalls. I'm on Windows 10 x64 if that matters.
I'm just really puzzled - I'd have thought that running two cards at the same spec would've yielded the same hash rate on either. It isn't the end of the world that they're different, but part of me really wants to know why there's such a big difference!