Technical Question XJ650 VS XJ750 differential gearing ?

I have acquired a rear differential and rear wheel from a xj750 to use for the bigger brakes. I noticed when installing that the 750's splined flange that interfaces the rear wheel to the differrential was different. I exchanged the two to get by. My question is this.....
which "rear end" has the better gear for gas mileage? I hope to use the best milage gear setup and then install a jet kit to pick up more power. (stage 2) offsetting each other hopefully. I get ~ 47 running the hell out of it on the interstate ~ 80 miles a day.

Added a 750 front end to get the dual disks up front, stainless steel lines, replacement master cylinder and the bigger brakes in the rear, all new bearings front and rear, new steering bearings (all balls) ,all new shoes/pads, new front and rear tires. Now it kicks ass!

My only complaint has been poor bakes but no more!

Still looking for a font right tun signal assy 81 xJ650.

Paint job to follow candy apple green I hope!

George

 

BUMP
Robert can you move this to the Mod forum?
Thanks...
G