Isn't 6700/7900 the point where they changed the pull ratio of the front mech, so ST-6700 shifters won't work with FD-7800?
Done a bit of researching before purchasing as I wanted to upgrade to 7900 DA levers but those have the issue you pointed out, apparently 6700, 7800 and one other that I can't remember are all fully compatable. The braking has changed, but I've also read it's not even noticeable.
I'm sure slightly vague braking should still be no problem in this relatively flat UK...
Done a bit of researching before purchasing as I wanted to upgrade to 7900 DA levers but those have the issue you pointed out, apparently 6700, 7800 and one other that I can't remember are all fully compatable. The braking has changed, but I've also read it's not even noticeable.
I'm sure slightly vague braking should still be no problem in this relatively flat UK...