I took the 2x 46/30 + 11-42t cassette yesterday to the mountains and the 11-42t definitely made the hard climbs easier. In fact the same trail I took I did with a single speed 34:16t (had to walk the bike on some portions), on my 2x + 11-34t (still hard), 2x + 11-36t (less hard) and 2x + 11-42t (hard, but grinded while retaining the most energy and according to my heart rate monitor I did the uphill with the lowest BPM). I also installed a new chain with a KMC X10. Big/gig also clears if you accidentally go there, but I would not ride in that setting. Shifting wasn't as smooth throughout the range, but once I hit 11-42t on the steep uphill, I definitely felt like it made a difference. In fact I think with this same setup, I can tackle the same mountain trails that are mostly reserved for MTB'ers. A couple of things to note: the clutch really needs to be set in the OFF position, if not shifting becomes very rough; since this was a bit of a shake down I had to make multiple stops to adjust the derailleur, though I came home and re-tweaked everything. Overall for the intended purpose of how I ride bike, I think I'll settle on this gearing setup as being the best for my urban roads/mountainous terrain.

My final thoughts being, if you need the low gearing I think the GRX 400 and GoatLink will get you there, but with some convenience trade offs. Before going that route though, I do think the max spec'ed 11-36t cassette for the GRX 400 should considered for the smoothest and most compliant shifting and lighter weight. I hope this helps anyone else in the future looking to go this route!