do you have 1600 G.Skill at 1.9v and if so is windows reporting it at 1.3Ghz instead of 1.6Ghz.
also do you get post boot errors for VGA bios?
Off topic
Windows has always reported what i have set it to, no issues there at all
Had some issues with it stopping at VGA bios but this has usually been unstable overclock attempts (I.E me trying for 4.5/4.6ghz!)
My stable overclock (in sig) boots first time every time fine mate.
/Off Topic
back on topic CSS is a very CPU dependant game and again E6600 is not the best cpu, granted def not the worst to have in your build either!
I bench the CSS Stress test at 700fps+ but in game myself (say in a 10 man match/pub) I will be between 250-500fps just dependant on the area of the map, players etc.
He certainly is not getting 300fps in game!