How Should I Scroll my Fafnir Angelic Shooter?

For anyone that cares to do the math, it would be way more helpful to see when 5 main and 5 secondary stat outdoes 3 atk in terms of:

weapon used (mostly, the multiplier),
%atk,
and %stats.

I'm pretty sure AB has a 1.9x multiplier, 15% ATT on my current weapon (Loveless Purple Dragon) but no other sources of %ATT.