How's the coincidence, I haven't been here for months and when I do show up I see a thread of mine ressurected.
Hi dragotron, welcome to the forum.
I won't beat around the bush, the 650i chipset was known to be an average chipset for overclocking so I don't fancy your chances of anything major, that said you "should" be able to hit 4.0GHz at or about stock volts so stock cooling "should" be OK.
Just remember not all chips are created equal. I have two E8600's at present and they both respond differently to overclocking.
What is the VID of your chip?
Also if you do intend pushing it I'd recommend looking into an aftermarket cooler, I still think the Thermalright Ultra 120 Extreme is one of the best coolers around and pretty decent bang for buck these days.
I'll check back in a day or so to see if you've replied