Originally Posted by
Camilo
Just look up the max sprocket size and max chain wrap for your derailleur. That info is readily available.
I posted links for the Shimano specifications for both GS and SGS models above. They're also listed in the 2019-2020 Shimano specification handbook.
Dunno if the OP has looked at them or not.
I suspect the OP may need a derailleur hanger extender ("goatlink" or equivalent) to use the GS with an 11-42. But it's at least theoretically possible he might get lucky without one.