So I got a PNW Coast Bar in 480mm. Just built up the bike a couple days ago and managed to get a couple rides in,one gravel and one road. First thoughts are this width, shallow drop and flare feels great for my intended use (60% mixed road, 40% gravel). Feels good and stable on the hoods and drops at speed and feels natural with my should width. Need to experiment with stem length to see the various impacts.
As it's a new bike with totally new geometry I can't really isolate all the variables.
If I was bikepacking or spending more time on steeper gravel I'd look at the 520mm but for day-to-day this seems to hit the mark.