Core 0, the core on the far left of RealTemp is probably the best of a bad bunch but there is no way to tell for sure. The 2 cores on the left appear to have some significant slope error where they change at a different rate than the temperature changes and core 1 has some issues with getting stuck at lower temperatures.

If you can't get one of these CPUs stable at 3.3 GHz then you probably have other problems besides core temperature. Run CPU-Z while Prime95 is running and see what is reported for actual voltage. Some boards are not great when it comes to overclocking Core 2 Quads and crap out when the bus speed goes over 400 MHz. I have an old Asus board that can run a Core 2 Duo reliably at a bus speed of over 500 MHz but falls on its face when trying to overclock a similar Core 2 Quad. I ended up buying a QX9650 for this board so I could overclock by adjusting the multiplier higher which allowed me to keep the bus speed at 333 MHz for better stability.