To answer your question, a couple fps depending on what kind of graphics card you have.
But what do you mean most P965 boards cant be oc'ed? The P965 chipset is great for oc'ing! The Asus P5B Deluxe, Asus P5B-E, Gigabyte DS3 & S3, MSI P965 Platinum, Biostar TForce965PT, just to name a few, are all awesome for oc'ing. The P965 chipset is just as good or even better then the 975X chipset when it comes to oc'ing.
And the 680i chipset and P965 are to completely different things, the P965 is an Intel chipset, the 680i chipet is made by Nvidia.