What chainring sizes do you recommend? I would like to use an Ultegra 8000, I read 50 tooth somewhere, but how would this run if a used Absolute black oval rings instead of standard round shimano?
You would be totally fine running a 50/34 oval on Flaanimal or Traildonkey.
It is definitely possible to run Absolute Black rings on the bike. Are you considering 1x or 2x?