We have a 2015 Calfee with Ultegra Di2. I wanted the biggest range possible. We're running 52t x 34t up front with 11t x 40t in the rear. We have a K-Edge long cage on the rear derailleur. This is probably far outside the operating limits of Di2. However, it shifts fine. My only complaint is the jump between the big & small rings is huge. Unfortunately, this is the consequence of a big range with only 2 chainrings.