Do not use a splitter where you split the 8 pin PCIe connector into 2 - 8 Pin PCIe, you are asking for trouble that way. Even if you properly undervolt, what will happen if one day due to some software bug, it reverts the voltage back to stock and you end up pulling more current than before. Very dangerious.
I will only add that vegas have an unpleasant feature. If the 8pin power is turned off but the socket power is saved, it will burn 100%.