I am not 100% sure but the Sphere Scroll Thyrus Caps are:

Accuracy : 35
Skill speed : 44
Critical hit : 44
Piety : 33
Determination : 31
Spell speed : 44
Parry : 44

So we can't add 44 DET and 31 PIETY but max 31 DET and 33 PIETY and with the remaining 11 points we could spend them in Accuracy but the result would be in a weapon a little better than Yagrush. Is it worth it?
Maybe is it better go with 44 Spell Speed and 31 DET?