VMMC-KLAS is 6350 nm via great circle. Obviously it would depend on winds but Gulfstream has validated more than 5000 nm at .90M and just over 7000 nm at .85M so VERY rough math my WAG would be about 14-15 hours going and 12-13 hours coming home. Actual mileage (hourage?) may vary.
Eff that! I'll stick to my little plane. I agree that the 550 is a sexier bird.