nvidia 590 mother board with Core 2 Quad compatibility

Hi everyone,
I have an nVidia 590 SLI motherboard with a Core 2 Duo E6700. I want to upgrade my CPU, could anyone tell me which is the best Intel CPU which is compatible with this motherboard. I know the Core 2 Extreme is out the question... im loooking at the Core 2 Quad 6700 at the mo ... is it worth upgrading to this from a E6700? I really cant be bothered for a new mother board so any advice would be much appreciated.

Should i overclock my E6700..?

Rig Specs
Dell XPS 710
Core 2 Duo E6700
4 Gig 667 Mhz Ram
Nvidia 590 SLI
500GB Raid 0
Nvidia 9800gx2 - currently installed
Nvidia 8800 GTX
Vista 32 bit
750W standard Dell PSU
2 Optical Drives

I'd check with Dell -- they'll know for sure, since it's their MB and BIOS versions vary between manufacturers.

PS - If you don't have the 8800GTX installed, there's not much point to listing it in your rig specs.