I5 2500k turbo mode when oc'ing

ive been trying to do a small oc my 2500k just to 4ghz as im quite new to oc'ing but although ive got it stable at 4ghz which i understand is pretty easy and the temps stay in their high 40's in prime95 im puzzled as to why the turbo mode seems to re-enable itself when i change the ratio in the bios so in effect windows and the bios only see the chip at 3.3ghz but cpu-z sees it as 4ghz !!! im using an asus p8z68-v and 4gig g-skill ripjaws x. any input on this would be appreciated thanks - jb

Windows will see it as 3.3ghz because that's the default settings and the "name" of the cpu, not the actual speed.