All intel non-K cpus can be overclocked to 400mhz
more than their turbo boost. Of course they need a P67 or a Z68 mobo.
Here you can see a few tips how guru 3d overclocked an non K processor:
Core i7 3820 processor review .
And here are a few things about you processor from intel:
core i5 2300
So you can see that you can achieve something like 3,1+0,4=3,5Ghz and this is only possible by messin with the multiplier and you can gain some more by messin with BCLK frequency.
This is also an article for non-K from xbitlabs:
Intel Core i5-2500, Core i5-2400 and Core i5-2300 CPU Review .
But in the end it shouldnt matter a lot to gain a couple of...