What a Noob! My PSU (Everest Pro 1200) has six 12v outputs (3x6 Pin & 3x8 Pin) each giving 20A so when using two of these (2 of the 8 Pin) the card is only getting 40A max. The PSU manual says it will give a max over current of 35A so not sure why my 590 would not suck it to the limit. Still I have just used a 2x6 Pin to 8 Pin adapter thus giving up to 60A, there is a noticeable FPS averaging at least 10FPS more on three tests i have done. Also used memory has gone from 800MB to 1300MB, so convincing me that this was a PSU issue. Right now i'm considering a new PSU as this PSU will only give a max of 90A on the 12v lines, so if i get another card i'll need a beefier one.