playing crysis is asking a whole lot, and unfortunately no, it will not overclock to play crysis. to find sum acceptable speeds, google geforce 6600 overclocks, and see what other people have achieved for a starting point.
rivatuner is a great app for overclocking graphics cards and personally my favourite, adjusts shader clocks, core clocks and memory clocks so everything you will need. it also has a inbuilt artifact scanner to generally test whether your overcloks are acceptably stable. of course after you run this for say 5 minutes, they ingame test is always needed to make sure its stable enough.
