7800 to 6800 won't likely improve shift quality. More like a lateral move. But you get the newer, larger hoods which IMO are an improvement over the 7800 generation stuff and of course the new stuff looks better. Braking is probably better with the new calipers.
It's your money but 5800 is an even better value and I doubt you could feel the difference between it and 6800.
And 5700/6700/7900 shifts very good with the new 11sp polymer coated cables installed but I wouldn't bother with it at this point. If you already owned it that would be a different story.
Last edited by Dunbar; 09-05-14 at 02:24 PM.