I have in my posession three i7 motherboards and 2 i7 920 chips. The motherboards are as follows:
Asus P6T Deluxe
eVGA X58
Gigabyte UD5

Unfortunately, there are issues with all three card types:
Asus P6T: At overclock speed (192 BCLK), this motherboard will not go into S3 sleep mode in Vista 64. The TurboV software will not allow the BLCK speed to be dropped to a sleepable speed (160 or so) from within Windows.
eVGA X58 : This board will not sleep at overclock speed but will decrease to 165 bus speed via E-Leet software. The problem is that the overclocking in E-Leet is corrupted any time the motherboard comes out of sleep mode.
Gigabyte UD5: This motherboard will S3 sleep at overclock speeds and will also lower to 165 BCLK speed via software. The problem with this motherboard is that the speedstep setup is not keeping 21 multiplier within MSFS X. I see multiplier jumping between 17 and 21 while FSX is working at less-than-optimal performance.

All 3 motherboards overclock both chips to 4GHz. The Asus board runs MSFS X as smooth as can be at 1280x1024 res with an ATI 4850 video card. Getting that same smoothness on the eVGA and Gigabyte boards has been a bit of a challenge so far.

Nehalem users... please share the experiences with your motherboards.

Wingo,
With the exception of the S3 sleep mode issue at overclocked speed, the P6T was one of the easiest to overclock and most stable motherboards I've tried.

Are you overclocking? I used 1.35 volts for vCore, 1.35 volts for qpi, 1.96 for CPU PLL and pretty much left the rest on auto (but looked at memory to be sure it was clocking properly). You should easily get 4Ghz with that chip, but a top-quality cpu cooler is essential.

If you're running at stock BCLK, your S3 sleep mode should work just fine. It works okay up to about 160 or 165 bus speed and then doesn't work above that.

You're going to love the performance in FSX!

We all have different needs with our computers. I buy a machine which is most suitable for MSFS X, because that's my most demanding program I run, and then I use my computer for work the other 98% of the time. Since my computer room is in Hawaii and air conditioned/dehumidifier to protect 3,000 books, heat is as big an issue as electricity, and S3 sleep is an absolute requirement for me, along with fast, overclocked performance for my FSX sessions.

NickN, I'll be watching for sleep-related video driver issues. Too bad EVGA's E-Leet software is adversely affected by S3 sleep, but I bet they fix it in a future BIOS revision. Not holding my breath on the Asus, though.

Hi ENM, I am still using the Gigabyte UD5 board and it's working well now. I see some jumping between multiplier 20 and 21, but the results are excellent at an overclock of 3.95Ghz. I suppose a change in BIOS version may have helped. You might consider such a move if the problem persists.

For those who are following this thread. I have just installed the latest bios FC and no longer have the beta intalled (FC6). FSX now runs without any stutters, so this is the fix.