OK, let's suppose that two total flight crews are hired and all 4 pilots are type rated on both aircraft. The cost of initial training and recurrency would be the same regardless for a GV. I haven't checked, but would assume that a 757 type rating would be in the ballpark of a 747 rating.
If the limit of type ratings for each pilot is held to only 2 types, would this overburden the pilots with training, systems study and emergency procedures? The examples given by both of you guys (JJ and 411) include at least 3 types, which I imagine would be difficult and no fun.
I'm looking at roughly 800 hours total per year for both types, which is about 400 hours per year for each crew member. Would 400 hours per year be a good balance of time spent flying, and time made available for system study and procedures familiarization, plus some time to relax with the family?
Looking at costs only, I'd prefer to hire only 2 crews, but if it comes down to safety issues and crew satisfaction, I'll hire 3 crews. With 4 pilots, I'd still have a 3rd crew member available for the GV for the occasional long haul overseas, but these should normally be planned flights and not spur of the moment flights.
As a side note, I do wish that Gulfstream would fix the reliability issues with the GV. That aircraft will need to have a very high dispatch reliability for my needs, plus I'd hate to see the pilots having to deal with constant MEL situations and schedule changes because of the aircraft's unavailablity due to maintenance issues.