My car uses 36 lbs/hour at 65 mph in fourth gear and 32 lbs/hour at 65 mph in 5th gear. So that is the difference due to gear ratio.

My rear end ratio is 3.54 and 5th gear is 1:1 while 4th gear is 1.23 so this test is equal to a 3.54 rearend vs. having a 4.30 rear end.