I have a 2x 34/46 up front with 11-40 in the back on Apex Rival 1 rear derailleur with an extender. Works fine. Haven't considered going larger in the back, yet, but I think there might be some more room. But at that point you have to consider chain wrap capacity.
Edit: my rear derailleur is a Rival 1. Couldn't clear the 40t cog without using an extender.
Last edited by tFUnK; 01-19-20 at 01:37 AM.