In my 96 GTS (Headers, K&N, Borla) my best time with stock rear was 12.1 at Pomona. With 3.54 I hit a best of 11.9. Other factors may apply, but that was my experience. Most drag racers will say it should not make a big difference, and some may disagree. The jury is still out. I would not buy the gear for drag racing, as it is not as strong as stock, and puts additional load on drive train, however for driving on the street, it transforms the car into a much better, and more exciting ride.
If you are ever in San Diego, give me a call, and I'll give you a ride in my SRT. You can decide for yourself.