3.73's if you don't plan on racing the car alot. the biggest reason for the loss in mileage besides the increased cruising rpm is the driver. With the new gears you'll be using the throttle alot more to play with the car. It will be so much more fun to drive that the loss in mileage isn't that big a deal.
As far as launching an auto at the track, you 'll probably be doing different things depending on the stall. For the stock stall, you'll pretty much want to just brake torque it a bit to preload the suspension and hammer the gas at the last yellow. This will change dramatically if you are running street tires. With street tires you'll probably spin them pretty well so feathering the throttle to reduce the spin will be necessary. With a higher stall, sticky tires are almost a necessity. You can flash the converter which means to just stab it from an idle which will cause it to jump up to close to its stall rating and then engage or brake torque it to the highest rpm's it will hold without moving and then go from there.
And when you run, just start in 1 and shift it to D when you get to your shift rpm's. Don't shift into Od, it will not upshift at full throttle anyways and could toast your OD band.