Just so people will know, I swapped a Moser 9" 3.89 gear with locker into my 95 Camaro from a 3.23 7.5 " Gm one. My car is totally stock with 100,000 miles on it. With BF Goodrich drag radials, and the 3.23 gear, the car went 14.32 @ 95.3 mph. After the rearend swap, I just ran a 14.04 at 98.2 (3.89 gear).
My dyno program showed about a 2 tenth potential increase, and I saw nearly 3 so I guess I am happy.
It cruises at 70 mph tacking 2700 rpm with 26.5 inch tall tires. I love this gear! I am not crazy about the locker Tractec differential that it came with. It clunks, clicks, and bangs into gear when going from park to reverse and into drive. If you want your car to be a pleasant driver, DO NOT GET A LOCKER! Get a limited slip like the Moroso brute strength (had one for 3 years and never slipped at the track).
Hope this helps you guys thinking about changing gears or rears.