That being said, I like to run and keep my Core i7 920 at 3.8 Ghz for everyday, 24/7 use (though I can go higher if I want). I am currently cooling the CPU with my Thermalright Ultra 120 Extreme 1366, using the stock fan with an additional fan bracket and an Ultra ball bearing fan (silent and cools well) in a push/pull setup. DO NOT attempt these settings without proper cooling, so if you are using the stock cooler and/or have a cramped case this is not recommended at all!
Temps are fairly close to stock at idle (1-3 degrees more sometimes) and under load are only 5-10 degrees difference (In Celsius). It can pass all stress tests and never gets above 70 degrees even at full load. Here are the settings for the Core i7 920 @ 3.8 Ghz. My components are listed below.
Asus P6T Deluxe BIOS Settings for 3.8 Ghz overclock:
A.I. Overclock Tuner: Manual
CPU Ratio: 19.0
BCLK Frequency: 200
PCI-Express Frequency: 100
DRAM Frequency: DDR3-1603
UCLK: 3208 MHz
QPI Data Link: 7218MT/s
CPU Voltage: 1.30000
CPU PLL: 1.92
QPI/DRAM Voltage: 1.30000
DRAM Bus Voltage: 1.66
For CPU options, I turn off everything not needed including power saving, virtualization, and speedstep. You can attempt Turbo but I keep it off.
CPU Ratio: 19
C1E Support: Disabled
Hardware Prefetch: Enabled (Keep on for more performance)
Adjacent Hardware Prefetch: Enabled (Keep this on, too)
Intel Virtualization: Disabled
CPU TM Function: Enabled (VERY Important to leave on for protection)
Execute Disable Bit: Enabled
Intel HT: Enabled (Keep on for more performance, Disabled will run cooler)
Active Processors: All (If you have it, use it!)
Intel C-State: Enabled (helps your CPU run a bit cooler)
C-State Set Limit: Auto
Every other voltage setting is on Auto mode and I did not need to change anything else, including Memory timings. System runs like a top, runs slightly warmer than stock but fairly warm in intensive applications or stress testing. Passes Intel Burn test and Prime stable though.
If you have decent 1600 RAM and want to try settings out, let me know if they work for you but just remember these chips run HOT.
I can also run 4.0 Ghz but the temperature difference goes up enough to actually hurt performance slightly and not worth it for added stress on the CPU.
I am going to lap the heatsink and use a small amount of MX-2 instead of the stock Thermalright TIM and hoping to see my CPU temps go down even more but they are beyond acceptable even now. I do have a very well ventilated case which helps as well.