I test yesterday dps between garuda and ifrit and it was like 20 ~ dps difference. It is pretty small difference once your dps is around 800 - 900(combined your pet) with 15X gear. I think utility between garuda and ifrit heavily depends how you can utilize radiant shield and contagion. Other thing that can make difference is spell speed trait since ifrit hit 2x more often(because of auto attack) you have 2x better chance trait get procced with ifrit than garuda. Both garuda and ifrit is doing pure magical damage so you can not get boost from dragon kick or slashing debuff anymore. Need also more tests because parser can be broken as well.