This is a bit strange, but that stop 124 blue screen is suggesting RAM/IMC/Uncore-problem, but since you have passed memtest86+, your RAM should be OK.
So, probably it's a IMC/Uncore-problem (that's the equivalent of "System Agent" or VCCSA/VCCIO-problem on SB). This gets more likely when adding vCore doesn't help, and Prime Blend would react to that too.
Make sure your LLC is not bugging tho. Intel recommends standard LLC.
EDIT:
Try to run a
HyperPi32M, that's a good and fast test for pushing Uncore/IMC.