I'd stack Spellspeed primarily for CD reduction alongside faster casts of Ifrit spells and Ruin/Tridisaster during Titan phase for some Uunga buunga Tri/Ruin > Topaz > Fester/Painflare > Mountainbuster chainspells. And maybe you can fit in another GCD during Bahamut/Phoenix.

If a concern is raid buffs then develop a strategy around that if you have a static.

I'd personally just stack Crit though. Seems to be where the big damage comes in.