I don't have a 750, I have a 500. Red, a guy here locally, owns 2 750s.
All I can say is I really enjoy my 500. There's no drawback on the 750, it's just bigger than the 500.
minor annoyances (don't forget my user manual thread!) are that the opening of the pit is not big enough to get the cooking racks in & out. So I have a constant struggle trying to do that and have yet to come up with a consistent and easy way to do it.
there are others, but in general these are minor- meaning I would buy one again, and likely buy a 750 if I had the chance (and loose change!).