I am shooting a new bow this year. I have built new arrows both in 5/16 and 11/32 cedar. I thought one would shoot better but not so. Both shafts fly like darts field points or boardheads don't matter. I don't have a gr. scale so I'm not sure of weight. For a selfbow this thing aint so pickey. I'm happy about that.  :D  
I have never shot 5/16 before I may just go with them for that reason.

23/64 - now thats a shaft.....

QuoteOriginally posted by BobW:
23/64 - now thats a shaft.....

I like 5/16", usually spine is the problem but if I have a bow that will shoot them I'm all over it.  Shoot mostly 11/32" though as you might imagine.

Sounds like you are good to go.  

I feel the same as Slow bow.  Still have some 5/16 forgewoods and some hickories that are spined heavy enough for my bows, but I'm slowly running out of them.  11/32s are my next choice.  Talking woodies, of course.  5/16 is on the large side for a lot of carbons.

If both arrows are well tuned and of equal weight, I think you would see better penetration with the 5/16's.  There will be less surface area making contact, creating friction and slowing the arrow through impact.  That being said, a heavier arrow will show more penetration.  It takes more to stop a wrecking ball than a baseball.  

My cedars all weight around 470 grains.  Therefore I have selected my hunting shafts based on the quality of the wood grain.  BTW, I have mounted them with 2-blade Eskimos and tested their flight, just to make sure the pretty ones fly well.