Rorschach – I’d probably go Dt240’s, sapim cx rays,Oddessey taperlock nipples (alu bmx nipple you CANNOT round off) on Pacenti TL28’s.
For an all-mountain wheelset? 240’s are for XC and I’m not too sure on the Pacenti’s long-term durability. I’ve been holding off buying some for my bikepacking bike, let alone a trail/AM bike.
OP – I’d go for the Arch EX, I think Rorschach is thinking of the normal (old) Arches when he says they’re too narrow.
Most wheelbuilders will steer you away from bladed spokes/CX rays for AM use. They may be light and strong but they don’t build the stiffest of wheels.