Newbie..need a little help...

First, I just want say hello and Thank You to everyone in advance for helping me. I just purchased a sweet resto mod 1969 Impala. She has a 383 stroker with a turbo 400, 2500 stall with the electronic passing gear, 12 bolt eaton posi, 4 wheel disk, CPP 2" drop spindles, 18" and 20" Billet Specialties wheels, a/c, 2.5" exhaust with Hooker jet hot coated headers inside and out and 3.08 gears. I drove the car from Nebraska to Orlando about 1,500 miles.....she ran real easy with them 3.08's, not one cliche. But now that I'm home, I was toying with the idea of possibly changing up the gears. With the info I have provided about the car...what would you guys recommend.... 3.42 .... 3.55 or with the 20" tires,Turbo 400/2500 stall on a 3,800 lb car should I leave the 3.08's in. I'm just looking to get a little more off the line umph with this car. Thanks again and any info would be very helpful and greatly appreciated.
Jay

Welcome to CHR. The Turbo 400 is a non-OD transmission, so your final drive ratio is 1:1. You need to figure out what you want for your cruise rpm and go from there. I use the formula:
Cruise RPM = (mph x rear gear ratio x 336)/tire diameter in inches

Right now if your rear tires are say 28"OD you get (70mph x 3.08 x 336)/28 = 2587rpm. If you change to say 3.55's, then you'd have 2982rpm, getting up there. For me, I'd probably keep the 3.08's for cruising, or look for an OD tranny if you want to get taller gears for more pop in your acceleration. Taller tires will help drop your cruise rpm, but will hurt your acceleration.