You are looking at numbers as the same but all those little differences add up to quite a bit different frame. The BMC fits big and stretches you out a lot. If you aren't flexibile and top tall you are going to have a bad time. I know the di2 is attractive but I think you are chasing parts instead of a frame that fits. If you could fit the 54cm bmc with a longer stem and seat set back a little I'd consider it, but that 57cm is big.