I agree with rolli59. I would have ran them on seperate rails. If you run them both on the same rail, they have to share that rail's 25amps. To give them each 25amps available, they need to be on seperate rails. Search for 6870 amperage and you should be able to see how many amps they use under load. Actually, I just googled myself and apparently reference 6850's max out at about 11A. So crossfired they'd max out at about 22A. Technically you'll be just fine with both of them on the same rail.