[wstrayer]

In the years that I shot cedars, I never noticed a difference in weight if the shafts were the same spine. If it was a 65# 11/32" then the weight was comparable to a 23/4" shaft of 65# spine.
Wood arrows vary in weight even within a spine and shaft diameter. That is what separates good shafts from not so good. I found that if you can get woods to vary less than 50 grains within a single dozen, they will fly nicely for you.
Likewise good shafts can be purchased within a tighter spine range. Spine variation is more critical than weight. I can add more sealer to lighter shafts in an attempt to get weights closer, but I cannot add spine.
As a general statement, the 5/16" will be easier to remove from targets, but the difference in diameter will also affect your center shot.