The AMD HD 79xx series utilize a sunken die configuration making it problematic to have the flat copper coldplate of Asetek-manufactured closed loop coolers have consistent contact with the die.
For nearly all HD79xx series cards, we recommend using a copper shim to bridge the gap between the copper coldplate and the GPU die for maximum performance.
There has been reports of some non-reference HD79xx not requiring a shim, but unfortunately we are unable to test every board partner's board design or compatibility.
You can test your compatibility by installing the G10 and removing the cold plate to make sure the die is contacting the block.
If you require a shim, Performance-PCs.com sells an EK copper shim for $3.95 here.