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 !!!