Thanks for the replies.
I am have run ESXi 4 and am now running ESXi 5. I have run Win 7 Ultimate for a test period and experience the same locking up issues.
After an amusing, but embarasing on-line chat for Intel support, I was told that the RAM I chose from the supported list was not valid because no one had made a processor that supported the combination. Interesting given that it was on the recommended list, ie how did Intel test it. A question that Intel support was not prepared to answer. Anyway after leaving that chat confused, disappointed and a few hundred dollars poorer I went and bought 24Gb of cheap G Skill memory. I have now had the board working with only one similar locking event from 2 weeks since my original post. The original memory has been tested and works with two other boards that run DDR 3 memory with the same X58 chipset. Hence I'm stuck with it!
My lesson learnt for $300 and a lot of frustration, don't believe the list of supported RAM on the Intel site. One its clearly wrong, and two Intel themselves say it doesn't work when pushed! I would have been better off with no supported RAM list as I wouldn't have gone and bought expensive RAM in the first place!