What Steve W said. I am a Motorsports manufacturer with a capital M. There's a reason that 90+% of all 911s ever sold didn't come with an LSD from the factory. With the rear engine design the car has great on throttle traction. If you don't race your car, or track it once or twice a year, your money is much much better spent on tires, brakes, and the nut behind the wheel, not necessarily in that order.
In short, you don't really need an LSD.
Where an LSD, in a 911, really shows it's stuff is in the braking zone. We are talking pedal to the floor 140mph down to 50mph to drive through a 2nd gear turn. Without it the 911 wouldn't be half the racecar that it is. I'm not kidding. People are very very skeptical when I tell them that half, or more of the time gains they can make by installing one of my LSDs is because of what I can do for them under braking. And then they come back and tell me that I wasn't feeding them some line to make a sale. They tell me I spoke the truth.
Here's an interesting thread for you all to read. The modern GT3 comes from the factory with an LSD, a mud and ice LSD. I rebuild and retune them and consistently, time and time again, find guys 2-3 seconds a lap in DE cars with no other change than the LSD.
How do I do it? Because almost all of the performance gains they are seeing is in the braking zone with greater stability. The factory LSD does all right on throttle. It doesn't do squat (pun intended) under braking. The thread is not for the feint of heart. We are talking 13 pages of reading here:
LSD buster - Rennlist Discussion Forums
And yes, while it's focused on the 997 chassis, it applies to every single 911 ever made.
Have a good evening,
Matt