How much gaming performance will I get from E8400 3.0GHz to 3.8GHz+?

Hi,
I am Very much gaming freak guys, so I build the following configuration for my new Computer so please let me know how new high end games will performs.

Intel C2D E8400
EVGA GTX 260
Antec 900
G.Skill 2x2GB 1000MHz
ASUS P5Q Pro
Xigmatek S1283
1280 x 1024 resolution (yes I know a GTX 260 for that res is a bit overkill, but I like to max everything out)

My one more question is, since your not supposed to overclock any PC parts right away, how much slower will my games be at 3.0GHz with this setup?

If you are only concerns about Performance then At your resolution not a lot:mellow:. Its all about the video card in most games and with that low resolution you have no issues in that area. You might feel minor improvements in game "smoothness" and loading times but nothing earth shattering.

Go ahead and run that thing up to 3.6ish and see how it feels. Usually it takes some time to experiment to find stable settings at a max overclock and you can do that as you use the machine. Its a great way to stability test by doing a tweak and then use the machine for a couple of days and then tweak again. Or bang some numbers in and see what happens.

Which games you will be playing? If it happens to be TF2... you'll see performance gains all the way up to 4.0GHz (and probably beyond) because it's not multithreaded at all (at least I did).As you might be knowing that performance varies through the games...

Fallout 3
Far Cry 2
Left 4 Dead
Crysis
Call of Duty 4/WaW
Devil May Cry 4
Brothers in Arms: Hells Highway