Don't fall for the hype. From everything I have seen there is no power difference between a 65mm and 67mm. I have the 67mm and make nearly identical power to those with the 65mm.
1+++
I did a test on a dyno with the dual 67 and just picked up 3hp and lost 8 lbs. The 168 KB has to make a change both the 65 & 67 almost fit inside of it...LOL.
Manuel