Any gear lower than the stock 3.27s will help, and the GTs do quite well even with the stock 3.27s for that matter. I had 3.73s, they did a bit of a number on the mileage with my auto GT, 4.10s, 4.30s, even 4.56s are great if you plan to be on the drag strip a lot, but if you want to drive you car on the highway, and you want to get decent mpg, don't go for anything lower than 3.73s, that is my advice, but if you want to get it to the end of that 1/4 mile fast, sure, go low, go 4.30s or 4.56s, just remember its going to cost you at the pumps.