In case anyone is wondering, on a Sora 9-speed derailleur, you can fit a 42 tooth sprocket and a 11-42 cassette with no issues. Shown on a 2016 Trek Crossrip Elite. : r/gravelcycling
SunRace 8/9/10/11 Speed 11-40/42/46/50T MTB Cassette Bike Derailleur fit SHIMANO | eBay
Accessoire vélo,Ensemble de vitesses 1x10 pour vtt,dérailleur arrière 10 s 11-42-46-50T K7,chaîne pour pièces - Type 10S 42T Set - Cdiscount Sport
Mechanical Monday: How low can you go? Lower Gearing Options for One-Bike-to-Rule-Them-All, Part 1 - Cyclocross Magazine - Cyclocross and Gravel News, Races, Bikes, Media