I'm using precisely the same combination as you!
There are a couple of things to consider when discussing the Core i7 and maximum temperatures. First, the "maximum" temperature you will get depends heavily on how you load the processor. Everest's stress test doesn't get a chip as hot as Linpack. Linpack gets it less hot than Prime95. Finally, Prime95 doesn't get it as hot as Intel's custom burn-in tool. Intel's tool can push a processor with basic aftermarket cooling at stock clocks up to TjMax (which is 100C in the case of the Core i7).
In any case, I personally use Prime95 to check my temperatures. I will push 90C with Hyperthreading enabled (turning it off will reduce your temperatures quite a bit, usually about 10C). Keep in mind though that while my system runs 24 hours a day, I have never seen it exceed 65C under any daily use (usually gaming). Even transcoding doesn't push my processor temps up anywhere near the level that Prime95 does.
From my reading the chip I have is fairly "average", or maybe slighly above average, as an overclocker. I'm going from memory here, but hopefully the names of the various settings will be close to what's in your BIOS. My settings are as follows (Core i7 on an Asus P6T @ 4.00GHz)
AI Overclock: Manual
CPU Ratio Setting: 20
Turbo Mode: Off
DRAM Clock: DDR3-1600MHz
CPU Voltage: 1.35V
CPU PLL Voltage: Auto
QPI/DRAM Core Voltage: Auto (for the record, this SHOULD be called the Uncore Voltage, and not the ridiculous name it has in the P6T Bios. You may need to bump this up a bit to stabilize your system, particularly if you BCLK is over 190MHz. I wouldn't go much past 1.3V though)
IOH, ICH Voltages all on Auto (you might want to bump up the PCIE IOH and ICH voltage a touch if you're running Crossfire or SLI, but I haven't found it to be necessary. I wouldn't go much more than 0.1 or 0.2V over stock)
DRAM Bus Voltage: 1.64V
DRAM REF Voltages: Auto
Load Line Calibration: Enabled
CPU Differential Amplitude: Auto (I messed with this a bit, but didn't get much out of it. I could be stable at slightly lower Vcore, but my temperatures actually got worse)
Spread Spectrums: Disabled
Clock Skews: Disabled
You really should have good aftermarket cooling to push an overclock like 4.0GHz. I feel as though I may be pushing my luck, but since my real-world load temps are well within spec (under 67.5C for 99.9% of use, and 45C at idle) I'm not too concerned. Do check your temps carefully with Prime95 though, just to be sure. For the record I'm using a Corsair H50 with two fans in a push-pull configuration, and Arctic Silver 5. If you're using Arctic Silver or a similar paste, don't forget that they often take ~200 hours to set, during which time your temperature could drop as much as 5C.
Good luck, and have fun