shimano compatabliity?
 

I cannot read those charts to find this answer. I know some of the issues like braking performance can be less using the 6600's with the 6700 group. I am upgrading to a 6600 G double shifter and have a 105 on now. I cannot seem to find a compact 6650 new but would a new 6750 work without any drop in performance. I could just wait till a 6650 shows up on e bay I manage the 6600 shifters new for $175 so I was please.
Finally, the 105 I have is working really great and it may not be that big of a deal.
Thoughts? I have an ultegra FD now if that helps.