I play a frost garg build and gargs / fetishes (ambush rune) do proc Frostburn. My experience is that Frostburn are a must both in term of damage and CC. Rimeheart is really bad though. With my Necro build i get 75% frost damage (hands, shield, bracer, neck) but there is an intern CD on Rime that is superlong. I prettymuch permafrost packs but it procs rarely. The damage isn't that great either. SMK+ furnace (cubed) is much much better.