I just overclokced my CPU. Need advice.

[Castout]

Hi everyone,

I have the following system specs

Intel Core 2 Duo 2.0 GHz
DDR2 800MHz 4x2Gb RAM Memory
Nvidia 9800GTX+ 512Mb GPU

with the above specs I had a Vista experience index of 4.8 which was capped by the CPU. Core 2 duo didn't come cheap when I built my PC then as it was just released.

CPU : 4.8
Memory : 5.3
Graphics : 5.9
3D gaming : 5.9
HDD : 5.9


Now instead of buying another CPU I overclocked my CPU from BIOS.
So now I have an equivalent of Intel Core 2 Duo 2.4 GHz CPU. That is a 20% increase.

This boosted my Vista experience index from 4.8 to 5.3 out of the maximum 5.9.

CPU : 5.3
Memory : 5.3
Graphics : 5.9
3D gaming : 5.9
HDD : 5.9

My question is: Is it safe to overclock my CPU for as much as 20% without installing additional cooling hardware?

Thanks