Rob,
That is what I have found on my setups. Having a stiff enough arrow so that I can keep it full length allows for 28% EFOC right out of the box.  
I am pulling 31ish inches anyway so there isn't much arrow left hanging out.

I can cut off 1/8 to 1/2 and bump FOC to 31%+ Ultra EFOC.

Measuring from nock groove to end of shaft is correct.

i am shooting arrows by a small company named forge. they seem to be very strong arrows, i have only shot them for a short while, have done little stump shooting with them but i have shot several trees straight on and glancing shots and i haven't broken a shaft yet. and the guy i lease from has shot them for awhile and he is a dealer, he said they are the strongest arrows he has shot and that they are made with kevlar, they do not advertise the kevlar part on the website.
yes they are extremely light gpi, i pull 29 in and have several inches hanging over, i suspect that i could go down from 7.8 to 6.9 gpi arrows and cut them off and they would be plenty stiff then i could add the extra 31 grains to the front and get a 35-40% foc arrow. but they are pricey arrows so i got the ones i KNEW would work.

Very interesting.They sure don't give any hints on their site,where a person can get them.Do you know any dealers that do mail order?

bm22, are you shooting Slipstream 60's?

Nope, extreme 50-70's, email him they will ship you some. I think the public cost is $110-120 a dozen

Thanks.

ttt

ttt