Your car is going to hate highway driving. My hybrid, with a GS-R 5th and the stock 4.40 final drive, I'm doing around 4000 rpm at 80 mph. With the higher final drive, that numbers going to go up. I don't have the math infront of me, but my guess would be 4300-4400. You will accelerate quicker with the lower final drive but it may not be the most useful thing on the street. I would consider an LS 5th gear to help keep those rev's down (odds are, you'll never be racing and using 5th gear). Seeya.