My apology for the thread necromancy...
I have a pair of carbon fiber blades and I found that they were off by a fair amount. Luckily my other hobby is chemistry so I have an electronic balance that is accurate to 1/100g. I found that one blade was 7.90g and the other was 7.81g. Sure, 98.9% matched, but there was a noticeable amount of vibration. I taped the wing and got the COGs dead on, both blades sitting at 7.90g now.
I still have some vibration when spooling up, but this could be due to the blades not yet being pulled straight due to centrifugal force. I have balanced the flybar as well, but it didn't help much. Overall it is noticeably smoother than it was before balancing the blades.
The big issue I have is with blade tracking. It is spot-on at the moment, but if I swap the blades (like put them in the opposite grip), it goes about 4° out of tracking. Maybe there is something amiss with my blades after all.