Oh thanks for the reply but I have finally solved this problem.
It all started 2 months ago with this new cpu on a new ASUS board and I could never solve the issue. When it came up on my new MSI mobo with the same cpu, I feared the worst but I have managed to iron it out this morning by adjusting my cache ratio and boosting VCCSA, which is something that made no difference on the ASUS.
So the end result is that for all other stress/bench tests, including XTU, IBT, AIDA and Folding there is no problem running a modest 4.7Ghz OC with 2400 ram but for the Fire Strike test I have to dial the ram down 1333
I drop down to 4.6Ghz for my daily build so it's all good now. I am now confident of pushing this cpu further when I submerge it in the coming weeks