Any opinions on undervolting the cards ?

If I set the power limit to 90% they will use 135W * 6 = 810w
iNTEL g3900 CPU is 50W
mobo Asus PRIME Z270-A
+risers

Isn't this safe enough ?

Does running dual PSU come with other issues from your experience ?
Is the adapter all you really need for running it, as long as you keep the risers and gpus grouped per PSU ?