There won't be much in the way of overclockable kernels for a while. People won't be able to add that to kernels until Samsung release ICS kernel source code, and that'll happen when they've got a ROM ready to release. I'd say you're looking at March/April.
And why bother overclocking? Underclocking I can understand, as it can help to save battery, but overclocking serves almost no practical purpose.
I've been running FixeROM since last night, and other than some issues with the Contacts app it's working quite well. I might try replacing the Samsung email with an AOSP version, as I like the new gmail app look.