I’ve not flown both but have spoken to guys who have!
The 650 is nicer to fly on approach as it is much more responsive in roll - the Global can feel a bit wallowy at times!
This May be down to the slightly higher approach speeds, but much more likely to be that the Gulfstream wing is much stiffer. The Global wing is very flexible and gives a much more comfortable ride in the cruise...
If you want detailed perf comparisons, I have perf calculators for both types.