My springs are set up at 250-260 seated and 600 ish open With pushrods that are 9.750 effective length. The guy at Manton assumed I was gonna use 3/8 pushrod and said the stage 5 .120" wall but I said a 7/16 will fit my exhaust and and we went with stage 3 ..120 wall straight 7/16 on my exhaust but on the intake there wasn't much room for that on indy ez heads with harland rockers and B3 correction kit. I made room for a custom taper pushrod form manton thats a stage 3 7/16 to just a few thousandths smaller than 3/8 at the top under the cup with a .168" wall thickness after a lot of clearancing the pushrod areas. Manton told me the same thing everyone else here says. The bigger the diameter the better for stiffness, wall thickness doesn't do much. He said the same as far as ugrading to the stage 5 material as well after I asked. Most people say my pushrods are overkill though lol.