Pretty sure a 2016 SL6 500 series carbon and 2017 ALR are similar weight to one another. In that case the ALR could possibly be a lighter (or close) bike out of the box with the groupset difference.
I own a 960g carbon and a 1050g frame aluminum bike (lightweight alum like the ALR).
Personally as a first bike (and perhaps first foray into clipless?) i would go with the ALR w/ Dura Ace. Carbon seatpost and fork on aluminum bikes do a swell job as is, and you'd only be a carbon handlebar away if you even want a more muted cockpit. That's personal preference territory.
Personally i feel Aluminum gets a bad rap because most peoples experience are with entry level, heavier, lower-end trimmed ones...or super stiff race bikes like the CAAD which are designed for those that like that sort of feedback from their race bikes at the expense of some comfort. All indications and reviews point to the ALR being a comfy bike. I personally find my TCR Alum very comfortable, light and stupid fast, and if anything wished the Ultegra 6700 on it shifted as nicely as the DuraAce 9000 on my carbon bike. Cant go wrong with either at the end of the day, but i like the ALR Dura Ace here as a first road bike. My 2 cents....
Last edited by Esthetic; 12-26-17 at 11:28 AM.