I did some math for Dark Knight weapons, and this is what I found for their AP:

i210 Deathbringer 276.546
i210 Nothung 280.101
i220 Sephirot w/ x2 Crit 4 melds 305.135
i230 Hellfire w/ x2 Skill Speed 4* melds 317.614

*Reason I used Speed instead of Determination here is strictly for AP. A Det 4 meld gives 6 det where a SkSpeed meld give 9 speed. Even though Det is worth more than speed, a Speed 4 meld actually gives more AP than a Det 4 meld. Det does have secondary support, such as healing, Tier 5 Det melds make up for this and offer 12 points of det with Speed 5's 12 points of speed, so obviously THIS would be the better meld. But for the sake of this comparison, I tried to keep it simple and what would most likely be melded for these weapons.

A 12-point gain between i220 and i230 seems worthwhile, in my opinion, even if you pick up the ugly secondary of Parry.