A Global's speeds are 18 knots slower than a G450, but only a few knots different for landing than a G550. The takeoff speeds on a GLEX are lower than either one, owing a lot to the low Vmcg (86 knots) and some to the slats. The G550 has some more range, if you fly 6,000 nm legs frequently. The Boss ALWAYS likes the room of the GLEX.
GF