31-38*C for the chokes under full load? (Just to make sure we're talking about the same thing - the ferrite blocks with R68 written on them to the IO side of the CPU socket).

Mine are way over that. I'd say 45-50*C by guessing and touching. I'm running a W3570 at 4.3GHz @ 1.237v and have my PWM freq set to 500KHz, what do you have yours set to? You on water or air? Is there any airflow over that area in your case?
Yes we are talking about the same thing. I'm WCed using the same block and loop arrangement as you. Using an Obsian 800d case (air flow sucks) so I do have a fan that is blowing cold air into the case inside of sucking out as per original design, running PWM at 500 as 1000 didn't seem to buy me anything.
Water temp in the loop is 30c at its hottest.
Glad you found the source of your boot problem! They sure don't make boards like they used to!! Recently put together five crunchers for WCG and ended up RMAing two boards, both GB's within 2 months of install.