Do you think the axel to axel measurement...
 

Has an effect on the spine of an arrow? I think so. If you have 2 seventy pound bows but the ATA is different doesn't the longer one increase poundage more gradually.

I haven't shot any of the shorter bows so I have no experience to go on, but my 38.5 ata bow with a 340 arrow for the most part always seems like it's to stiff.

If there is some truth to it that would help reduce the guessing about which arrow/spine is best.

RE: Do you think the axel to axel measurement...
 

Don't know the physics but when I moved myG5 from my 36.5 to 31.5 I was shooting 30yds off my 10 yrd pin. The shorter axel seems alot faster to me.

RE: Do you think the axel to axel measurement...
 

Speed has also got to have some thing to do with it. It would make sense that a heavier arrow would effect spine.

I don't know how they come up with spine charts but If I did oneI'd err on the side of stiff/heavier just for saftey, then again I think GT's are the opposite to get the shaft lighter (their sales pitch).

They sell arrows according to poundage and supposed speed/cam, a heavier arrow effects speed. If speed is a factor then picking the right spine should include that not just what cam you have.