I ran a 9" with 35 spline axles, a spool (total drag car) and the rear housing was braced. The car weighed 3018 w/driver and made 1000+ Hp, 1.20 60". Ran 14/32 slicks and never in 12 years did I see any signs of twisting an axle. BTW make sure the axles you get are streetable
Here's an intreresting chart on axles
http://qp.doonce.com/axle_tech.htm