You won't get a huge CPU overclock on stock, but the 955 could probably hit 3.6-3.8GHz, it depends on your chip.
The 5850 can be flashed to a 5870 BIOS, which will give you 5870 clocks. Then, OC it more.
It should run WoW maxxed at 1920x1080. Crysis should run almost maxxed, just keep AA and AF low.