Tried out Tufo Thundero 48mm which are measuring 49mm on my rim. Plenty of Space on Fork an Seattubes...Only Place which is getting a bit closer is chainstays with about 5-6mm in each side...but this should be fine!
so the official tire width is a bit pessimistic and up 50mm should be fine
I have Caracal Race tires and they measure 50.8 mm on these wheels (32IW)
I'm planning to put Thunder Burt 2.1 on for the autumn period. I don't ride in the mud anyway, and when I measured, there was still room. I also measured Dubnital 2.0, but they're again tall like MTB tires and so-so. Schwalbe is about 53mm on these wheels.