I have built and ridden on wheels with butted Sapim spokes. I agree with Joe that they thread harder. I always use brass nipples to avoid stripping the nipple shoulders at the higher stress. When ridding often and hard, I found the did not hold true as well as DT or Wheelsmith spokes. I have the feeling they tend to stress relieve under use, even though I was carefull to work out stresses during building.
San Dimas, CA