The whole point of the Falcon 8x is not to go fartther and faster, but to have a 500NM range increase and a permanent crew rest while achieving the same take-off and landing performance as the 7x.
By re-designing the wing, Fassault have managed to save 600lbs, so the 3000lbs MTOW increase of the 8x is practically all fuel, meaning you can still operate to London !!!!ty, Cannes, La Môle, Saanen, etc....
Dassault's problem with the 7x/8x right now is dispatch reliability and product support, both of which are significantly behind a G550 for example.