Thx for the reply spoony. I exclude a PSU problem, I have a Corsair HX850W Modular which is great, and was connected to a Rampage II Extreme before with an i7 920 @ 3.7Ghz and 1.376 Vcore stable and I had no issuea at all with the previous build.
Anyway the hardware was this
Rampage IV Extreme
Core i7-3930K
Noctua NH-D14
3x Corsair DIMMs in Triple channel set @ 1866Mhz (they are rated up to 2000Mhz @ 1.65V
http://www.corsair.com/memory/intel-memory-upgrades/triple-channel-intel-memory-upgrade-kits/cmx12gx...)
1x OCZ Vertex 3 120
2x Western Digital Caviar Blue 320GB in RAID0
2x HD 6970 (but I installed only one card)
1x Asus Xonar DX Audio Card
Oh and I rebuilt my previous system using the same PSU and guess what? Everything is working fine and there are no issue at all on the 8pin ATX connector of the Rampage II Extreme.