Below are screenshots of CPUz showing the highest overclock achieved with each motherboard. Note that the ECS Z77H2-AX is absent from this section as we couldn't overclock it. We haven't been able to determine why this board doesn't play nice with our Core i7-2600K processor, but we suspect a BIOS update is in order. The results were achieved using 1.450v and the highest clock multiplier/base clock each board would accept.

Asrock Z77 Extreme6

Gigabyte Z77X-UD5H-WB

Intel DZ77GA-70K