I have done the exact type of shooting your describing, my camera of choice for this has always been the 645 Mamiya, I shoot with a leaf shutter lens that allows me sync at any speed and use a old Vivitar 285 and a strobo frame and it works great, my % of keepers is always far more than the losers.

The Pentax 6x7 is a great camera, but I find it a little heavy and un-weildly for this type of work.

Dave Parker
Ground Glass Specialties
Satin Snow(TM) Ground Glass