Planning to buy a Sandy Bridge system, then this roundup from OCC may be of help, although none of the motherboards the site tested seems to be bad as they all received a Gold award.

"The overclocking on the Pro gives you many options as to how you would like to go about it. There are software based options, BIOS based automatic options and manual BIOS options to choose from. We chose the manual BIOS based option to fine tune the overclock for our tests. The i7 2600K in the ASUS Pro overclocked with relative ease to a mind bending 4.951 Ghz clock speed with a controllable heat output. The vcore voltage was elevated to 1.48v in the BIOS and the core temperatures never exceeded the low 60's during the testing. This is quite remarkable seeing as how the last generation of Intel processors were known for their enormous heat output that required high-end cooling solutions when overclocking, not even to their maximum potential."



Link: Overclockersclub