Originally Posted by RiceAWay

If you look at Dura Ace Di2, there isn't a lot of difference. The Dura Ace levers are so light that they might float away. And there is a small difference in the weight of the crankset. But so small as not to be much. Otherwise the derailleurs are the same weight and you can get lighter cassettes than the Dura Ace. Since you're using Di2 there's not much problem with shifting on different cassettes.