its not lagging to far behind a sandybridge pentium Dual core
now when you get into higher levels of overclocking, you have to worry about temps and voltages and a bunch of complicated stuff, but since your running a dell, you won't be able to change most of that, which means you won't get a very high OC which means you probably won't have to worry about temps getting too high
a CPU has its core freq. for the e8400 its 3Ghz, deeper than that it has its Front Side Bus, nearly everything runs off this, so when changing this changes a lot of things.
the FSB for the e8400 is 333Mhz, for its Qaud Data Rate (QDR) its the FSB times 4, that is which the speed your ram runs at, in this case 1333Mhz
now you get your core freq. by the FSB times the CPU core multiplier, in this case its 9
so when you change your FSB from 333 to 340 it changes the core from 3Ghz to 3.06Ghz and the ram to 1360, now that isn't much, but it will be better than stock
you can probably raise the FSB higher than 7, but I would not raise it higher than 15 (348) because you might not have enought voltage pumping to it and you ram might not run stable at that point, but no permanent damage will occur you're OCing in software, the worst that will happen is that you have to go in safemode and disable the settings on boot up
some tools and information