I have ridden neither of the disk versions. But since you've been a week without any replies . . .

Last year, I owned and rode a BMC TimeMachine 02 with Ultegra Di2 and the old Dura Ace (2-button) auxiliary shifters. I liked the bike a lot. It was very comfortable and stable and I found it very easy to perfect my aero position on the bike. I was extremely fast on that bike and I wish I still had it. Since the TimeMachine hasn't changed, except for the addition of disks, I would have no hesitation recommending it for you. Excellent bike.