Any 12" and smaller notebooks/netbooks have a fraction of the gaming performance of the M11x. The SU7300 is also a lot more powerful than the Atom or Athlon Neo CPU's.
The most powerful for gaming would probably be the Eee 1201n with dual core Atom and ION graphics, then the HP Mini 311 with single core Atom and ION graphics.
The Toshiba T115D-S1125, Acer Ferrari One, and MSI U230 are all in the same league, built with ATI/AMD, has better CPU's than the Atom, but slightly weaker GPU's than the ION. But I think they're better rounded machines than the Intel/Atom machines.
The Ferrari one is unique in that it has AMD's XGP port. It can hook up to an external GPU like the one made by Fijitsu. At CeBit, or one of them shows, Acer showed an external box with the F1 that had an HD 5870. I have seen fraps of Crysis being played on the F1.