Its been so long since my LGA775 i forgot so much, haha
also you can easily pick up an C2D E8400 for about $20 amazon, i have done this many times and they all worked (if you are looking for something a little better)
even so as for this CPU and overclocking it,
it looks like you cant disable speed-step, thats needed to be off because speed-step regulates the FSB, which is needed to be manually set by you to overclock, if speed step is not off then you can try but the OC may not stick. (check on boot with CPUZ to see if it is off or not)
Personally i wouldnt try anything over 3.2
An EX OC) to get 3.0 ghz, you would have to set your FSB to 12.5 * 240 = 3.0 and raise the Vcore a little bit.
as for your VCore, it needs to be raised to maintain higher overclocks, dont go past 1.4vcore, be conscious of your temps, dont let it get too hot.
To overclock raise your FSB in increments of 5-10. when you reach a point that your PC crashes during (prime95) try to raise your VCore a little bit and try again. keep doing this to see whats your maximum OC and when you find it take your FSB down 10.
i was a noob back with my 775 and I didnt break it and i got some nice OC's. I forgot most of what i know since I upgraded years ago. if anyone knows better then please feel free to correct me
this is some articles i found i hope you find it useful
http://www.overclock.net/t/1058898/p5kpl-am-ps-e5200-oc
https://www.techenclave.com/community/threads/ocing-e5300-on-asus-p5kpl-am-ps.81797/
http://www.tomshardware.com/forum/255954-29-e5200-asus-p5kpl-overclocking-issues
good luck to you and your endeavors, i hope i can help, and sorry if its not simple enough or too simple, idk your skill level :/
take care