Originally Posted by mjfwk

As always - I can't find the reference I was after

If you read Sheldon closely, he talks about stretchy spokes protecting the rims, not being more fatigue resistant themselves. The only spoke he describes which would be less prone to break is the DT Alpine III, which is triple-butted and is thicker at the hub end than a regular spoke.

Zinn outright says straight-gauge for heavy riders, but gives the reason that butted spokes stretch and loosen more easily than straight-gauge. But the online shops advertising wheel building and having spoke options listed show straight gauge spokes as being the choice for heavy riders (> 230lb). Velocity built Deep-V training, Dyad touring and Tandem wheels all have straight 14 gauge spokes - only the road racing rims come double-butted.

And lastly - from personal experience of having had a wheel (Sun CR18 rim from memory) rebuilt from straight gauge to DT Swiss double-butted - the wheel became 'flexy' around corners when heavily loaded, kind of like riding with a flat tyre. And it still broke spokes. When it was straight-gauge, it broke a spoke at the thread, which is supposed to be unusual, but it never gave that flexy feeling.

Edit: O.K. - there is some wheel testing info on Harris cyclery showing that all things equal, a straight-gauge spoked wheel is stiffer than a double-butted spoked wheel. But I also found a recommendation for heavy riders from a professional wheel-builder, and he claims that a triple-butted spoke will last about three times longer than a straight-gauge spoke. So - skip double-butted and go triple-butted