Ok, I'm at work and bored off my rocker, so I came up with this. I apologize if someone's done it before....
We all know its terribly inefficient for a necro to twitch a cleric, but what about a cleric twitching a shaman? I didn't bother to look up actual numbers, because I'm just being silly, but;
Cleric spends 400-ish mana to CH a tank for 7500 hp in 10 secs
(750/sec) net loss: 400 mana
or...
Cleric spends 400 mana to CH a shaman burning SC for 7500 hp
Shaman burns 7500 hp to heal said tank for 25000 (5 * 5000) hp in 25-ish secs
(1000/sec) net loss: 400 mana
Now someone clean it up and go post it on the cleric forums