[bobcowan]

The 8.8 is plenty strong enough. Unless you plan on drag racing with big sticky tires and power adders, the 8.8 will last just about forever. Using a 9" rear increases weight and parasitic loss.

For street use, stick with the stock Ford limited slip. The price and availability is good, and it's a good unit. If you're going to be road racing or autocrossing, step up to a worm gear, like T2 or TruTrak.