I am using 80% let-off.Yes the more let-off you use the slower your bow will shoot but you will never notice it though.

Funeralplanner I did notice you are shooting a lite arrow.I do realize its 5 grains per pound giving you 345 at 69 lbs.Just a word of precaution,you are shooting the lightest arrow for your setup.
Are you shooting this setup for 3D?
And please dont shoot any lighter or your warrenty will be void on your new allegiance should something let go.None of my business,just a word of precaution.