I have Holden 2000 with the ls1 and the same trany. I need to put 3.91 gear ratio and some guys suggested for 3.73. One of the guys told me that the diffrent will be only 100RPM between the 3.73 and 3.91 ration. My car is A4 the car is not for highway drive. Only twice a week.
Please need help here

 

The gears you need will really be dependent upon which size tires you are going to run and what RPM you want to be hitting as you cross the traps. To help you make the choice you may want to play around with this link a http://www.f-body.org/gears/