E6550 overclock freezing problem. Plz Help!

Hey guys.
I've overclocked my E6550 2.33Ghz @ 3.2Ghz w/ Zalman 9700LED which i think it's a really good cooler and also doing a great job right now.
i keep having problem w/ freezing which i dont understand. i know when it freezes, it means tht my overclock is not stable. But I can't find a reason why it keeps freezing. I ran OCCT for about 3 hrs earlier and it froze again.
Here are some things that i thought it could be a reason.

1. Temperature
2. Core Voltage
3. Ram

first of all, my temp is around 30' when it's idle and around 60' when im running Intel Burn Test or OCCT. is tht bad? i thought 60' on full-load is fine.
secondly, my core voltage is 1.36~1.38v. it stays changes around tht range constantly. i think it's enough. is it too much or should i give some more voltage to it?
lastly, i have 2*1GB Crucial Ballistix timed at 4-4-4-12 w/ auto voltage(around 1.8v). I ran memtest and didnt find any error. do u think i tightend the timing to much? should i loosen it to like 5-5-5-15? or like 5-5-5-18?

I really wanna figure this problem. Please help. Thank you.

oh, and also, would changing my E6550 to E8400 be a big upgrade?

and according to synthetics benchmarks there is not much of a difference..
http://www.tomshardware.com/charts [...] U,370.html
gaming wise +10fps on supreme comander
http://www.tomshardware.com/charts [...] r,397.html