Ok, I've read something about this kind of glitch.
First of all, base speed for 2 weapons is supposed to be (left wep's base speed + right wep's base speed) / 2.
With the glitch, it will become (LWBS ×3 - RWBS) ÷ 2.
So Stormlash (-10) with Griswold's Redemption (-10) should be (-30 + 10) / 2 = -10.
And then add -30 from Stormlash, -40 from Gris and -60 from Shael x 3, then your attack speed will be -140. Is this correct?
As the base speed is slower the better, then Schaefer's Hammer (20) seems a good choice.
(-30 -20) / 2 = -25
-20 from Schaefer, -40 from Gris and -80 from Shael x 4, you'll get -165!
Yes, you'd put Hel or -req jewel into Schaefer and make use of str glitch in this case, so you can sock 4 x Shael into Gris.
And your Str must be between 153 and 188, I believe.
I'm not sure if there is any difference between -165(Schaefer) and -140(Stormlash), even if my calculations are correct though