i would just leave it at 3ghz, you wont get much more from the extra .2ghz. Once you get past 1333 fsp your also overclocking your motherboard too so northbridge voltage may need to be bumped up. Also set your ram manually to 800mhz. you may just need more cpu voltage, cant remember what is safe for those cpu's. but yeah, should be fine at 3ghz. this program is easier to use http://sp2004.fre3.com/download.htm and you can load it up multiple times 1 to stress each core. prime95 only runs on 1 core.
Next stop should be a guide for your particular motherboard. Google is your friend.
Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the System Memory Multiplier (or whatever your BIOS calls it) from AUTO to 2.00, 2.00B, or 2.00D - whichever you need to set the Memory Frequency to twice the FSB. Then when you increase the FSB, the memory clock will rise in in proportion with it. At an FSB of 266 MHz, your memory clock should be at 533 MHz.
The 700i series is just a 600i that has been modofied to be compatible with the 45 nm Core2 quads.
So, at 3.0 GHz, your FSB freq will be 333 MHz, your FSB clock will be 1333 MHz (4XFSB), and your RAM clock should be 667 MHz for a 1:1 FSB:RAM ratio.
With your memory settings on Auto, at 3.0 GHz, your RAM is running at DDR2-1000 RAM speeds:
Your RAM settings are limiting your overclock.
Your present vcore settings and load temps indicate that you still have a fair amount of OC headroom.
Do not exceed vcore of 1.50 volts or load temps of 70 C.
iam, Prime95 has always supported multicore processors. Earlier version were a bit of a PITA to set up, but the later versions automagically run on all the avaible cores.