Why? If 5/16 work, why would you go with a thicker (possibly heavier) pushrod and potentially have clearance issues? I have used Smith Bros 5/16 pushrods in my last 3 engines, riding on solid roller and large flat tappet cams, no issues at all.
From what I’ve gleaned here and from tech Articles is that you want the stiffest pushrod you can fit, the Weight concern is typically on the valve side, so a heavier pushrod is not an issue. Again, this is strictly info Ive found here and elsewhere.
