Can't view photobucket here (at work), but I know the Core 2 Duos are monster overclockers from firsthand experience. You can probably get that chip up to 4 GHz if you really try. I've got my E6600 running at 3.5 on air, and got it as high as 3.7 (with major stability issues).
Just keep your temps south of 70C and you should be fine. Open that baby up!
You have very little reason not to juice up that system.
Let the temps guide you on how high your system can go. Start out at 3.6Ghz and do some testing, check your temps.
If everything is looking good bump it up a bit and test.
Keep doing that till you hit the highest temps you're willing to put your CPU through.
Only the actual performance will tell. It's a bit small and light compared to the better air coolers that have heavier heat sinks, bigger 120mm fans that push more air.
At NewEgg the customer comments for that cooler - one person said he had his E8400 running cool at 3.6Ghz.
If you are gaming with just a low res, just oc what you have. If planning on doing any fps gaming or video encoding, definitely upgrade. I think SC2 only uses 2 cores anyways, but anything newer will be able to utilize more.
E6600 here, (basically the same cpu, just one stepping before), running 400x8.
there is NO reason why you should not have OC your cpu already; shame on you!!
no srsly, go get that extra power, 3.6 should be easy for you.
FYI i have 1.38 V on the cpu and my cheap ArticPro 7 (now CM 212) never complained - NEVER had dangerous temps.
besides, gigabyte board.. it's just begging to be OCd
Good air cooler with a high end Core 2 Duo and a Gigabyte board is overclocking heaven. Back when my E6600 and GA-P35C-DS3R were new, they were absolute monsters. 3.5 GHz dual core five years ago was pretty damn nice.