I bent/twisted 2 stock shafts running mid 10s at 3700 lbs. You definitely need a good one at your level. I'm currently running a 3" dia. steel "thickwall" shaft made by my local HD truck shop. So far it's help up running 8.90s at 3900 lbs., but I honestly wouldn't be surprised if it failed on me. Everyone else at these speeds is running 3.5" dia. shafts.