Low Level Mage Specs for LFD

I spent some time this weekend running instances on my mage as part of my leveling efforts. I've been leveling as frost and have always been really pleased with the amount of dps I've been able to generate in instances. There's always been a little bit of a tickle at the back of my mind about what I'd be able to do with a fire build rather than frost. After all, fire is about throwing these huge fireballs at mobs that crit for enormous amounts of damage, so it should be a lot better, right?

What I found is on an overall basis, it didn't seem to make a whole lot of difference. While I was in fact throwing enormous fireballs in the mobs direction, and they were critting for a lot more than my frostbolts ever do, I wasn't doing it nearly as fast as I do with my frostbolts, and I was running out of mana much faster.

Here are the fire talents that I was picking up at level 41:

Improved Fireball 5/5
Incineration 2/3 (note, this probably wouldn't be in an endgame fire build, but both fireblast and scorch are good parts of my rotation at this level, so extra crit here is a good thing0
Ignite 5/5
World in Flames 2/3 - I originally took these talents because I was expecting big things from my Pyroblast - after all - huge ball of fiery death sounds so call. What a disapointment you were, Pyroblast. A 6 1/2 week cast time, and you don't do as much damage as my trusty firebolt. If I was redoing this, I'd probably put these talents elsewhere.
Pyroblast 1/1
Improved Scorch 3/3
Master of Elements 2/3
Playing with Fire 3/3
Critical Mass 3/3
Fire Power 5/5
Combustion 1/1

Now combusion is pretty cool - increases my crit chance and damage, stacking three times. The thing that annoyed me about this talent is that I have a somewhat similar talent in frost - Winter's Chill. It increases my crit chance, but not the damage. It stacks 5 times, but I don't have to push a button to get it going - it happens automatically. Plus, even my favorite AoE, Blizzard, will get that one going. On top of that, Ice Shards, on the second tier of the frost tree, provides a 100% bonus to frost crits with all three points - and again - no button to push and no cooldown.

So, after experimenting for most of the day, I decided to go back to my good old dependable frost build. While seeing huge fireball crits is a lot of fun, the frost build is so much more effective for leveling while you're waiting for than next dungeon to pop, that I think, at least for me, I'm better off staying there.