Optimal overclocking for Intel Dual Core E5200

[CntrlAltDel]

I'd like to know what is the optimal clock speed I should overclock my Intel Dual Core E5200 at, I mean optimal as in something I can leave my pc Idle on or general usage

 

[nna2]

do you have an aftermarket cooler? if not then the stock speed is the "optimal" frequency

 

[spentshells]

More details please like...... all of them