I'm running the carbon reinforced 10", for my hex I have some 11's and 12's. When I tried the graupners I was at like 70% throttle just to get it to hover using 3s batt carrying a hard mount gopro on my 450.
But then I see guys like you running a comparable motor tearing it up, very frustrating to me. Last time I tried graup's, the quad tipped on take off and chipped the very tip of a blade. I had ordered what I thought was one spare for each direction but what I have is 2 spares of the same direction, satisfaction did not live up to the hype for me so I'm either going to sell'm or throw them into the prop pile.
Yes 6mm is the size so you'll need either a 6mm to 8mm spacer for the graup's or go with the prop adapter Kloner linked to.