I built mine using an older Ultegra 1x11 mechanical shifting setup. The only issue I encountered was with the front derailleur cable. I had to file down the frame slightly for a better fit. The rest of the cabling went flawlessly. The handlebar was a bit fiddly, but with the help of a special routing tool, it was manageable. Shifting performance is quite good, and I didn’t notice any difference compared to non-integrated cable routing.

I have similar measurements and ordered a size S frame, based on a recommendation from Chris at Velobuild. My current road bike, a 2018 Stevens Aspin Disc in size 54, is also closer in geometry to a size S than to an M. I intend to use the new frame as an all-road bike rather than a trail-oriented bikepacking setup. I would also advise you to contact chris.