Actually, the M11x can be overclocked to 1.7Ghz without voiding the warranty, as it comes from the factory with the ability to do so. It is really a mickey-mouse overclock, though. More-or-less taking a true 1.7Ghz CPU and underclocking it so it can be sold as overclockable - all marketing from Dell.
If you get it, do the CPU upgrade option with 3MB cache, 4GB RAM Upgrade, w/ a 7200rpm hdd (unless you choose to pay another $350.00 for the SSD option). It is much better than the other optional CPU. It supports Intel's virtualization technology as well a few other features the 2MB cache CPU version doesn't. In addition to being a bit faster.
But yep, that machine is kinda weak for gaming. It is however, a slick little machine, as I almost got one myself.