Red devil rx580 8+6 power connection

[boatznhoes]

I have built around 13 machines but this is the first with these cards. I've never seen this before but they have a 8+6 power connection. Do I really need to connect the extra 6? Apparently this is so the card can pull 350w if needed.

Will it run on the the 8 pin (6+2) connection? The evga 1300 watt power supplies do not have sufficient cables (or power slots) to power 6 of these.

Advice?

[chohav]

It will run with only 8pin connected, few people from the forum have tested this already.
Just not sure if you will have some problems while mining for longer period of time and have some power draw spikes. So good undervolt is a must in this case.