I haven't spent much time trying to figure this out but I need too. I think the OP isn't worried about cooldowns he is worried about procs.

IE

http://www.wowhead.com/?spell=44549

Brain Freeze Rank 3
Your Frost damage spells with chilling effects have a 15% chance to cause your next Fireball spell to be instant cast and cost no mana.


If you miss the proc on this you miss the chance to send a free fireball.