Yup, Overspeed just goes DING!. I turn mine on at the track so I know when I hit 100.
As far as the oil leak, its a 2 day job, easily. If your car is a garage queen, then I would scope out the dealer and make sure you are ok with the technician that will be doing the job. I also would get under the car myself, perferably with the mechanic and view the leak & undercarriage. The LS engines are pretty well known for having bad rear main seals too. Nothing worse than having the car in for days just to find out 'that wasnt the problem'.