Great info! I should have said out to 500y (about as far as I want to shoot a 556). Certainly better long range performance with the ARC, but I don't love the 1 MIL of drop from 800 to 850.
I will say that the idea behind my 14.7" is to compromise somewhere between the 11.5" and 18" which I think it will do well (and the 14.7" is probably what I'll end up keeping if I can get the lighter bullets to a speed to help me hold coyote fur to 300y)