Moving this question to the Competition BBQ Forum where many people have competed and won with the WSM.
Member Jerry Aguilar of Burnin and Lootin was the 2012 California Rookie of the Year and came in 2nd overall in the 2014 California Team of the Year standings, cooking exclusively with WSMs.
Member Steve Aguilar of Vicious Smoke took GC at the Pechanga BBQ Championship with a WSM and was 15th overall in the 2014 California Team of the Year standings.
Our good friend Harry Soo of Slap Yo' Daddy BBQ cooks exclusively on WSMs, has won many GC and RGC awards around the U.S. and appeared on the first season of TLC's BBQ Pitmaters using the WSM.
Going back to the late 90s', guys like Mike Scrutchfield, Jim Minion and Jack Rogers, and Hank & Elizabeth Lumpkin were winning contests using the WSM.
Dig deep in this forum and you'll tap into lots of competitive BBQers and WSM competition info.