leaving on just causes lower temps, and power comsumption, and under load will jump as u said to the default clock speed of 3.4ghz. turning this off produces more heat but not alot as the cpu will be running at 3.4ghz all the time, it shouldnt have an effect on games as the should stay near the stock speed and not 800, if u feel its hindering ur performance or want full speed for reg usage then its a simple bios on or off option lol I leave mine off just because for me it seems a little more sluggish at 800mhz when im just in windows doing nothing lol but when it was enabled my idle temps were good and my 133watt went down to about 89watt, well they were good either way and if ur using the stock cooler shouldnt have a huge effect on how well it cools as its what its suppose to do