Can I crash the thread a little with my own, very related conundrum - Why not Rollei 6008 series?  May not work for the OP, as the wide angle lenses come pretty dear, but waist level auto exposure (as a side bar question is there a 645 that can do this?) Sounds like a real joy to use.  Similarly the backs and film advance sound good to me.  I'm currently using gs-1 which creates great negs, but for the predominantly 8x10 prints I make feels like overkill.