I have a Gigabyte UD3P and Q9550. Can do 3.6Ghz without special tweeking and temp never goes above 45c. I think I can pull 3.8Ghz without getting too silly with the tweeking.
This is WAY better than my Dual-Core E6400 which peaked at 2.8Ghz @ 65c.
Gigabyte is by far the best for OC (from what little I know), since that board has dual-BIOS. If an OC fails, it loads the backup BIOS and allows more changes to be made. I.E., very forgiving OCing.
The Gigabyte also has tons of tweek options, but you really need to know what you're doing while going beyond fsp, volts, etc.
Asus is good and has more software tools, but the Dual-BIOS makes all the difference. More so when a BIOS update fails !!!
I just upgraded from an ASUS P5ND to the EP45-UD3R. Wow, what a huge difference. My Q9550 is currently running 4.1Ghz at 1.30V, about 55C at 100% load on a cheap water setup. It has more in it, but it'll be a few weeks before I can test it because it's busy running statistics simulations.
The only downside to the board is that there are some wide gaps in RAM timing; so, you either have to have very good memory sticks with big heat spreaders, or you have to be willing to take a hit on RAM performance and step it down.