Balanced carbs are a must.If even slightly out they will cause vibrations.Although a bit costly at the time I'm glad I bought a Carbtune 2 years a go.It's of such high quality and ease-of-use I would never be without it but with it's build quality and the fact it is even serviceable I doubt I will need another in my lifetime.I went for the 4 carb one as it's not much more than the two carb one and had helped other biker M8s I have.
Remember when balancing carbs the trick is to set them slightly out so when you tighten the lock nut they come into perfect balance.
I have my carbs balanced to within a half bar of each other, and the bike runs really smooth, up until the band that I mentioned. However, that is also where the spark advance opens up on the ignitech.
Some people have mentioned balancing their carbs at a higher RPM, and then others say not to - I didn't, as I am not sure it is an accurate way of doing things.
I have been looking for larger grips - thanks for the link Shep, I might have to try those out, since they are pretty cheap.