If this is the case then 3.91's will put you closer to peak rpm in 4th as you cross the stripe, which is what you want. That being said I'm not sure 3.91's will make THAT much of a difference, or atleast get you to that peak point. I'd say 4.10 or 4.30's would probably get you there but those are steep gears for the street. I'm switched from 3.23's to 3.91's but have yet to run it yet, I'll be curious to see what the difference is too.
