Why not just use a 46/30 crank with an 11-36 cassette?
24/28 with 40mm tires is 23.77 gear inches.
30/36 with 40mm tires is 22.94 gear inches.
This would give you a 46t ring to still use for flat/rolling/downhill riding.
An Ultegra GX or a 105 rear derailleur thats mid-cage(GS) can handle this setup as its 40t total capacity.