You are using the white memory slots correct? Just checking.
That PSU Should be fine, unless it's faulty or has some compatibility issue (Which I've not heard any)
Do you still have the Gigabyte board? If so, what board is it exactly - GA-EX58-UD3R or GA-X58A-UD3R? And for either, what is the revision printed on the bottom corner by the PCIE slots? I ask because you may need certain BIOS for some of those boards/revisions to use 950 CPU. like Ex58-UD3R Rev. 1.0 must have F6 BIOS to use 950. So we need to know more exact specifics before would could say, but this may be the issue, and the same may apply for the Asus board you mention as well