Right now Unitrax makes two types of half shaft, the standard ones rated up to about 700 hp, the heavy duty ones for higher power applications. Personally, I snapped a U-joint on the BTR Viper half shafts while running on street tires, so I have switched to Unitrax.
Also, I saw a prototype set of heavy duty half shafts at Unitrax's shop in Anaheim. The will be good for the same 700+ hp range as their current heavy duty half shafts but will weigh substantially less. I'm not sure when they become available.