MND, VIT and PIE are already capped on Alkalurops. The remaining caps are:
+9 Spell Speed
+20 Determination
Determination scales much better than Spell Speed does currently, so that's the wiser choice to go for. I wouldn't worry too much about hitting those caps, but if you still want to, I would suggest either:
- Savage Might Materia III (4)
- Savage Might Materia III (4)
- Savage Might Materia III (4)
- Savage Might Materia III (4)
- Savage Might Materia III (4)
That combination will cap Determination and wouldn't be too costly either with the current Materia prices. The other choice is:
- Quicktongue Materia IV (9)
- Savage Might Materia IV (6)
- Savage Might Materia IV (6)
- Savage Might Materia III (4)
- Savage Might Materia III (4)
That combination would be perfect, though costly; and slot three could potentially cost you a lot of gil. If it were me; I wouldn't even bother putting any Materia in. The weapon still performs really well without any and it's just an inbetween weapon until you get your Thyrus.
Hope that helps. Good-luck!