E5200's are nice budget chips.. I once overclocked one to 4.3Ghz on stock air

I guess you could crank it up to around 3,6Ghz 24/7
Getting a Q9400 (and overclocking it) should pretty much double your WCG production.
Although I am doubtful the mobo will hold up to an OCed Quad for long.. just had a look at the P5KPL/1600, the VRM does NOT look good. 3 phase analog with no cooling whatsoever, I fear you might blow up the board crunching 24/7 with a Quad. At the very least I would recommend to put some mosfet coolers on it.
Maybe save up a bit more, and either go the AMD or S1156 route.