A faster processor or more cores for my Mac Pro?

I'm a relatively new Hitfilm user, have been using it with my Mac Mini server, but am about to treat myself to a Mac Pro. I've searched these forums for discussion on best setup for the new Mac Pro but can't find anything - odd?
My initial question is whether to go with the faster processor (with less cores) or the slower one (with more)?
But it would be nice to know what the support is like for Hitflim for the dual GPU's that come standard with the Mac Pro etc etc.