From my play experience as a Bowa, here’s the deal: To reach 7 FPS ias breakpoint, you have no gear flexibility using GMB, namely on helm slot. I had to use a Mavina’s socketed with 15% ias to reach it, while having a 14 fana aura Faith GMB.
So it boils down to this from what I understand. You need to have 13(95% IAS needed) or 14(92% IAS needed) fanatism aura minimum on faith and need all the right gear to reach 7 ias break point whereas a matriarcal bow gives you more options.
That said, I also read that even at 8 FPS breakpoint, your overall dmg imput is greater with GMB than Matriarchal…
Don’t hesitate to correct me if I’m wrong, but that’s what I read left and right, and that’s what I experienced when I was playing bowa, since I wanted 7 FPS anyways, I had no item flexibility.
EDIT: Diablo 2 Attack Speed Calculator | ias calc
I used this site to make my calculations.