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HOLY JEBUS!!!
Thanks for the info
notbatman, I've been missing out on big MH/s.
Going to try this ASAP and let you know if this has boosted my MH/s. Hopefully I won't have heat issues as am running full cover liquid cooled cards

Many thanks
Somebody said Windows might not like more than 5 GPUs without some fussing about, just heads up on that if you use that OS. Also my HD7990 is an AMD reference card.