basically, I was looking at the Dead Island requirements which say the CPU required is a Core 2 Duo 2.66ghz. I have a Pentium Dual Core E5200 overclocked to 2.8ghz and I was wondering how the performance of that would compare to the Core 2 Duo, and if so, how much might I have to overclock it more so it gets to the same performance? thankyou 
The requirements should not be seen as a hard restriction that won’t let you play the game. Don’t bother the game will run fine.
Ah yes, you can’t just overclock your cpu to make it faster than the E7200.
A strong GPU is much more important than your processor. What’s your graphics card and how much RAM do you have, and what resolution would you be playing at?
And a core 2 duo is actually quite a bit faster clock-for-clock than a Pentium Dual Core, but in gaming the difference should be negligible (maybe a few frames per second).
Good thing is, you can get low-medium end core 2 duos now a days for the price of chips second hand or new, so, waiting for your gpu and ram specs, might not be a bad thing taking the chance for a small upgrade