Others marvel at the great versatility of the G550 wing without resort to any bells or whistles...
Ha its just physics. A smaller wing with slats should be able to achieve better field performance AND better cruise efficiency. All else equal there would potentially be a tradeoff in terms of lower climb performance and engine-out performance, but thats straightforward.
It makes me assume that Bombardier and Dassault are terrible aerodynamicists. Their planes have slats and are also less efficient. If you take the max fuel and max range numbers for the G650 and the F5X, you see that the G650 uses only 16% more fuel per nm at its max cruise of 7,000nm @ M.85 compared to the F5X's efficiency at its max cruise of 5,200nm @ M.80. Considering how much larger, heavier built, faster and longer range the G650 is, thats a very small fuel consumption difference.