This is slightly off topic but you may find it useful information. My friend and I did and experiment comparing gargantuan enchanted spells with spells enchanted with unstoppable.
It turned out the fulcrum point was about 600 base damage. In other words for spells below 600 base damage, gargantuan was better, like link and power link. For spells with base damage over 600, unstoppable was better, like efreet and helephant.
If you add the infallible aura into the equation, I'm not sure what happens then.