Originally Posted by
kv501
Totally false.
I have 2 bikes setup with 5700 and 6700 shifters and derailleurs respectively, both with 5500 brakes. The "less than optimal" argument is BF fluff from back when Shimano said the pull ratio was different. There is no mushiness or any other "problems."
Having used 6700 STI's with 6600 brakes, then going to 5700 brakes, which have the correct pull ratio, there is a small but perceptible difference. Lots of things which aren't officially compatible will work, if you want to try, great, but performance will not be as the manufacture intended.