it should be exactly the same, the ultegra just weighs a few grams less. I would guess you could even mix cogs from 5800 and 6800.

I have a few hundred miles on this setup and it absolutely rules. the 50/34 12-28 gives me great range with excellent close spacing, I never have to shift out of the big ring unless I'm climbing, my most used commuter cogs 23/21/19 have a much more acceptable chain line, and I don't have to change a thing from daily riding to racing, because the higher gears are single step.

shimano needs to get on board with this, the 11t is useless for 90% of people who ride bikes. why not spec this on everything?!