I have the new RXL's..... DT 240's, DT aerolite straight pull spokes, pretty light, swapable endcaps, etc. I would highly recommend them. You can get 54-tooth star ratchets, which gives them a 6.67deg engagement..
The RXL and XXX wheels are a 24mm wide extrusion, while the Rhythm wheels are the wider 28mm extrusion. The XXX rims are pretty light duty.