If no spacer between the cartridges, I would adjust them just slightly looser that typical for a loose ball and cone bearing. You will kill the cartridges if there is side preload through the cartridge, and they are just not as sensitive to a loose adjustment as is a loose ball & cone.
One of the benefits I see to cartridge bearing rear hubs is that the pseudo-cone can help to reinforce and strengthen a wimpy 10mm threaded steel axle, less prone to bend and break compared to a loose-ball & cone axle which typically bend just inward of the cone.