low power or bad riser also sharing molex for risers or 8 pin pci e power cable can be cause of lower hash rate based on my experience.
Thanks for the response. This isn't really a dedicated rig so I've got the cards right on the boards, each with their own 8 pin PCI-EX cable coming from PSU
It might be that the board is just too old and isn't delivering the right amount of power as you've mentioned. It's a first revision Sabertooth 990FX
https://www.asus.com/Motherboards/SABERTOOTH_990FX/overview/Afterburner does report lower power consumption, but up until now I related that to the lower amount of work being performed..
I'm going to try to switch the cards to see if I can isolate it to a the second PCI_EX slot.. I know I have more than two but these are double slot cards so I'm limited in which slots I can use...