There's only a demo version of Crysis, and it's less optimized than the retail version. Crysis Warhead has no demo I'm aware of, but it retails for $30, and it's safe to say it runs roughly 25% more efficiently than Crysis. Impressive considering the graphics/physics have also been given a boost. Post up your specs/resolution you use and I can tell you if you can run Warhead on "Enthusiast" setting.
AoC is more CPU intensive being an MMO. The latest CPU's are about half the price of the latest GPU cards. Core 2 Extreme series is a different story though. No game requires one of those though.