You're pretty much wrong here, as the X1600 was used in all MBPs and iMacs for about 2 years...
As far as OC'ing, I don't think you're going to see much of a performance benefit, but the only way to tell is to keep pushing it until you see screen artifacts. Then back it down a notch, and see if you can get it to run reliably. Its really just a trial-and-error process.