Nice build. I am curious why you chose the 817 RD instead of the 815 when there is less take up on the 817 and the 815 reportedly works with an 11/42 cassette. I just ordered an RD-R815 for my bike to replace the 8050 GS rear, so now my remaining ultegra component is the front DR which will stay because I have a 50/34 power2max crank. I also have to say, I much prefer the metalic pads to the resin pads that come with the GRX calipers, they are harder on the rotors but stop with less hand pressure and fade less too. I do like the position of the hidden buttons on the GRX Di2 over the Ultegra and DuraAce location, nice change that I would bet will come with any new version of Shimano Di2s.