No it's because of your specific chipset. Some of them really suck for clocking.
Try and see if there might be a motherboard (hacked) BIOS out there on the web that allows you to change frequencies. When you do overclock your CPU make sure you've got proper case / CPU cooling installed elseways you'll fry that baby on the longer run.
A 4200+ should be able to run 2.8-3GHz.
Crysis is one of those specific CPU-hungry games. In general games where every MHz on the GPU's memory counts, you'll find an increase when you overclock your GPU. The problem with Crysis is the sucky coding or whatever that makes it eat any processor and still shows unpleasing results. Even if you buy a phat rig it's not playable on that so-cool 25xx x 1800+ resolution of your way too expensive plasma screen.
By that I meant to say: Crysis = no go for benching
It seems my system just hates overclocking.
