Hmmn, I used spokecalc for my first totally scratch wheelbuild where I did not know spoke length in advance (i.e. not a copy of an existing wheel). I calculated for 3X and they came out way too long. I restrung the wheel 4X and it worked out pretty well. Next time, I'll try a different calculator, I guess.
I don't know that there is a durability advantage to single (i.e. large) gauge spokes vs butted spokes. That would only be the case if the butted spokes were failing in the butted section.
On the other hand, butted spokes are inherently more robust, as a spoke is really just a very stiff spring, and a thinner spoke will exhibit less tension variation and arguably experience less fatigue than a thicker one, everything else being equal. That said, it would take some very intricate analysis or very meticulous testing to determine whether the difference is significant. Things I know for sure are:
- butted spokes are theoretically more robust
- butted spokes save a small amount of weight
- butted spokes save a small amout of drag
- butted spokes cost more to make