My power supplies have many 6pin pci-e cables but usually only two 8 pin cables. I usually prefer cards with one 8 pin and one 6 pin slots hence my problem :(. Is it safe for me to buy a 2x6pin pci-e to one 8pin pci-e adapter or even one 6pin pci-e to one 8pin pci-e adapter?
Thickness is important for minning. I would ask the seller the AWG of the cable. If your PSU deliver high AMPs, I would use 16 AWG and never would buy cheap cables online (I have melted a few of them trying to save some bucks with cheap cables).