I really wanted a BMC replacement at the end of the day and i had two main contenders on my list.
Super Six Evo or the SL4 Tarmac
Both are no brainer choices. Cannot go wrong with either but at the end of the day a special on a S-Works SL4 made up my mind. (incidentally i have recently borrowed a super six evo for a couple of rides and have found it to be an excellent ride but the handling is slightly twitchier for whatever reasons).
So i acquired the SL4 and started building it last year. Immediately i wanted to keep my Di2 grouppo. I know that it wasn't the newest any more with the 9000 range but it was still more than good enough for me. I wanted to take advantage of internal cabling on the SL4 so i was hell bent on getting it all internally routed. First problem i ran into is Shimano stopped stocking the internal Di2 cabling kits for the 7900 grouppo. Luckily, this allowed me to arrive at an even better solution.
I managed to find a custom loom sold and modified to include an internal seatpost battery as well! The OEM internal di2 cabling would have meant for the batt to sit under the BB. Internally within the seatpost is a much cleaner solution. Charging can be done via one of the cables outside the frame so you do not need to remove the seatpost everytime it runs out of batt. One of the other advantages are that the batt+custom loom saves significant amount of weight on the standard Di2 setup.
Spec wise, i decided to splurg a little and specced the bike up with the following components.
Enve compact 420mm
Lightweight bar tape
Extralite 110mm OC stem
POP headset cap
Specialized Romin Pro saddle
Aican Bungarus cabling
Titanium speedplay axles
Aurendel Mandible in Matte
Lightweight Milenstein Clinchers
Michellin Pro 4 25mm tyres
All said and done, the bike was around 6.1kgs which, i thought was fairly respectable given the non WWness of the SL 4 frame.