Sadly my CPU is pre-turbo so I have yet to mess with such a feature. One big thing is this though, do you have a reason for wanting the faster turbo speed? If not, then I would just recommend leaving it at Auto. I have come to learn in the computer world that unless you have a good reason to OC, its just not worth the trouble you can cause.
Edit: In any respect though, you may want to do it because you are a tinkering type of person. If so, then just set it to .1Ghz higher then the rated turbo and test it out. That will tell you how it works, without screwin the pooch.