Thanks, Keithskye, I appreciate the complement. I agree that a lot of "modern" aviators are brought up with little engineering instruction (that is, nuts and bolts of the mechanical bits) and perhaps even less on the aerodynamics and performance side. We have "dumbed" down a lot of it.
TunaHP
I should have added that the G550 with more wing area and lighter cruise weights probably has a 2000 foot altitude advantage throughout its cruise profile. That is probably worth about 300-350 pounds per hour fuel burn reduction. Doesn't sound like much, but over 11 hours, it adds up.
Why the weight difference? Again, the GLEX was built to a different brief and different FAR 25 standard. The GLEX has a more complicated wing-high lift systems and multi-function spoilers, it has 4 generators rather than 2, 6 hydraulic pumps in three systems rather than 2, and a larger airframe, which means more interior weight and so on.
GF