First off....someone said 3.55 or 3.73. NO WAY. You will hate your decision. I could see 3.73 on a roots blower since you see almost instant boost, but on a centrifical blower these gears are a WASTE of money.
Some other things I'll comment on:
1. Your gas mileage will improve in theory. But are you really going to put a blower on and then never go WOT.
My car isn't a daily driver and when I drive it I drive it to have fun. Won 6 races over the last week without even trying
Gas mileage will depend on driving style.
2. If you put the blower on and want to actually get the power to the ground, you NEED to get some drag radials for the street. I would vote on Nitto's since it's a daily driver and you will want some miles out of them. I now have BFG's, and I'll be happy to get 5,000 miles out of them.
3. I would vote on 4.10 gears for you. I have 4.30's, but my Viper T56 transmission also has a 2.66 first gear versus your 3.3X (can't remember exactly) so for me, it's like having a 4.10 in the car in first gear. Hope that makes sense.
I had 4.10's in the car when I still had the IRS and T45 trans and it was a lot of fun but I still wanted more.
4.10's all the way, or 4.30 if you are ready to get some big sticky tires.