Recently there was a "discussion" about the roles RDM can fill in the Omen thread. There were also comparisons made between the subject weapons. I have both and on a potency standpoint I'm sure Rdms agree a properly augmented Grioavolr wins.
My dream augment(without Dark Matter) for a Grioavolr would be:
MND+15, Magic Accuracy+30, Enfeebling Magic Skill+15
There's a small debate about how wide the gap is between something like that and AG Murgleis for Enfeebling Magic Accuracy. If we go by the idea that the we only get about half the value of Magic Accuracy Skill into our Magic Accuracy then we could math out:
Grioavolr: 114+14+30+15= 173
Murgleis: 127.5+40= 167.5
Pre-Omen the best pairings for each would be:
Grioavolr + Clerisy Strap+1(Magic Accuracy+15)
Murgleis + Forfend+1(Magic Accuracy+16) or if dual wield Colada with Magic Accuracy augment cap.
One of the common arguments for Murgleis is its AM1 but if you are playing backline it's not easy to maintain. If you're meleeing you give up the increased damage of AM3.
Post Omen we get acces to the Ammurapi Shield(Magic Accuracy+38). It is a dramatic increase over the the Forfend+1.
None of the above values take into consideration the gained Magic Accuracy from INT and MND.