Test with Ghom and my multiplier factor was the same as 2.74 as well. (My average ping is 250ms, so maybe that's why)
While 2.51 can't chain freeze a monster as effectively, it is very rare that you need to just chain freeze one monster (this includes ubers as well).
Off my head, I can only think of the following, but I can't chain freeze them with 2.74aps either (am using bone chill, does it make a difference?)
1. Treasure Goblin
2. A3 Keywarden
3. Ranged elites with fast affixes (Gobin shaman, sandfly etc)