Fumz

Whether or not you're able to keep SpeedStep enabled depends entirely on your board and how good its bios is. Intel has done a really nice job with their variant, so for obvious reasons, if you can keep it on, it's a good thing. AMD chipsets have always had problems with their variant, Cool N Quiet, with respect to overclocking and it's generally better to keep it off, which is unfortunate.

However, it's always good to keep in mind what it is you want the machine and your overclock to accomplish? If, for example, you can OC your cpu to 3.5GHz with SpeedStep and OC to 3.6GHz without SpeedStep, then you've got to weigh your decision. I would personally stay at 3.5GHz with rather than 3.6 without... mainly because at that point, that extra 100MHz isn't actually doing much for you other than giving your bragging rights; however, keeping SpeedStep enabled is doing something for you.