I don't know why you would want to go with higher gears. Mine only turns 2,200 - 2,500 rpm @ 70 mph.

If you went with a lower gear ratio (which would give you a slower top end speed) it would just about make first gear obsolete and your fuel mileage would go right down the toilet. You would only roll about 5 feet and it would be at redline (auto and 6 spd).With a 6 speed you wouldn't have to worry about it popping out of 1st gear because you would be starting in 2nd.