I forget where but I think it was an official SE release, one potential augment was Damage +4 on a Scythe (528 delay model, Death/Vassago's Scythe lookin' one). Since the delays are somewhat equal, it wouldn't be impossible to imagine Damage +3 to 4.
The +3 or +4 DMG augment seems kind of common, even on one-handed weapons for RDM or COR.
Job specific augments also exist, but they seem kind of weak. (RDM get +2 sword enchantment dmg).
So maybe +4 dmg, +3 acc, +2 to double attack for this GAX? There is also stuff like "water dmg +14" out there.