only a function of tranny gear ratios for each gear, differential ratio and "loaded" tire radius. Both the NA and TT 5sp tranny gearing is the same but the differential ratios are different and so is the tire radius. The stock TT 245/45-16 "unloaded" tire radius is smaller than stock NA 225/50-16 "unloaded" tire radius by about 0.1", thus probably not significant difference in loaded radius. The final 5th gear tranny ratio is 0.75:1. The NA has a 4.08 differential gear ratio and the TT has a 3.69 gear ratio. In 5th gear the NA has a total final ratio of 0.75 x 4.08 = 3.07 and the TT is 0.75 x 3.69 = 2.77.
My NA with stock tires (225/50-16) revs to about 2700 at 60 mph and about 3150 at 70 mph. Based on the TT total final ratio and neglecting tire radius difference the revs would be about 2420 rpm at 60 mph and 2825 rpm at 70 mph.
So if you want improved fuel mileage you need to put in the TT 3.69:1 differential or larger diameter tires (not recommended). Or enjoy the better acceleration and drive less.
