So I've been conducting my own "tests" since 4.4 dropped, and thus far my findings have led me to the conclusion that... Well, it's sort of variable. My raid static has two casters and two melees for DPS. However, we've found that while Garuda's contagion did assist my co-caster's numbers and the healers, overall my raid leader has helped me to confirm that Ifrit still seems to have somewhat higher numbers in terms of both my personal DPS as well as raidwide gains. Despite that, Garuda still has her place. We're presently working on O9S, and to ensure things go more smoothly during the Earthquake/Crystal phases I've found it safer to ensure Garuda's out beforehand so that Radiant Shield doesn't inadvertently go off and kill off the DPS by mitigating just enough to stop fatal damage from removing the earth debuff. Since Aetherpact is also dangerous to use in these phase, Contagion also becomes essentially your best bet for raid buffs at these spots, unless it would come off cooldown just after the debuffs wear off, in which case you might have time to Swiftcast Ifrit out in time for your physical attackers to benefit from RS.

In short, aside from certain specific situations, Ifrit appears to remain the more useful of the two for now. I wouldn't say what I've found is conclusive, exactly, but it's a start.