I too have used straight gauge spokes on 26" (559 mm ISO) wheels for years and my weight is 320 lbs. I have started building my own wheels and have just finished my front wheel - 27" Sun CR18 36h rim, DT Swiss Competition Double Butted spokes on the original 30 year old SanShin Gyro Master hub. I'm gathering what I need to build a rear wheel -27" Sun CR18 36h rim, DT Swiss Competition Double Butted spokes, an overhauled Shimano 600 Hub, and a NOS Suntour 8.8.8 Freewheel.
I'm using double butted spokes because I'm custom building my own wheels.
As to triple butted spokes, 1) they need a hub that will accept 2.5 mm spoke elbows and 2) Universal Cycles sells the DT Swiss Alpine 3 triple buttted spokes. They cost at least twice what double butted spokes do - $2.00 per spoke vs. $0.99 per spoke.