Once in the BIOS incorporate XMP prifil 1 speed memory is increased to 1600mgz and the voltage 1.65v. Otherwise, no XMP memory option "Kingston HyperX 4GB 1600MHz DDR3 T1 Series Non-ECC CL8 XMP" works perfectly on 1333mgz. However, with increasing frequency with the XMP 1600mgz drastically increases the temperature and the CPU. Intel i7 860 at full load is not exceeded 50c and now at idle (only built in OS) reaches 46-48C. No XMP temperature return to 28-30C. At full load the XMP temperature is reached almost 80C. Currently I have all returned to normal. I installed the new BIOS F6A.
Set your voltages manually. Or, easier still, change your memory multiplier. With the i7 860 you can set your memory multiplier to 12, or whatever is appropriate for your board, and run at 1600. Still a good idea to set your DRAM V to the factory spec.
What V does the RAM run at when XMP is disabled? It doesn't make sense that your temps would raise almost 20C just by turning XMP on. Sounds like too much V is being sent through when you enable XMP. That's why I suggested manually setting the BIOS values.
I don't have a good answer for you. If the only thing that changes is that the RAM multiplier is increased and the V goes up, you shouldn't see that much change in temp.
Next time you test idle & full load - with XMP on and XMP off - see what CPU says your Core Voltage is. Be interesting to see if for some reason when under load the Core Voltage with XMP on is different than with XMP off.
My motherboard is a Gigabyte P55-UD3. To measure temperature, I used RealTemp, Speccy and readings from the BIOS.
The Prime95 showed temperature 80-83C. When you touch on the CPU only warm. CPU cooler spinning like a really temperature 80C.
Per previous suggestions, I checked the CPU core voltages with and without XMP active. without: RAM 1333mhz and CPU V: .896 WITH: RAM 1600mhz and CPU V 1.136.
"In summary: So after my detective work, I figured out that the heat difference while idling was caused by differences in CPU core voltages while idling. The differences in idling voltages are related to the CPU idling clock speed. For whatever reason, with the Gigabyte P55-UD3 board, when the RAM is clocked from 1333mhz (auto) to 1600 mhz, either by XMP or manual RAM clock increase, the CPU does not downstep while idling. It stays at 2.8Ghz, or a 21 multiplier. Conversely, when the RAM is at 1333Mhz, the CPU generally downsteps to x9 multiplier (1.2GHz) while idle. Thus, in turn, lowering the Core voltage and with it, the CPU temperatures. A solution? If you need to run your RAM at 1600mhz, I'd suggest getting a program to manually control CPU clock speed and downclock when you're idling."