That's really the crux of mages (and a few other classes) in the latest patches/talents. They rely on procs to achieve their maximum DPS. They all do good damage, but it really comes down to what is easiest for you to try to multibox with. Ideally, I would probably prefer fire spec through 3.0.9, but I realized that I wouldn't be managing my procs all that well.

Before Lich and the changes that brought Arcane Barrage, which finally breathed life into arcane specs, I was mostly arcane, but a lot of points into fire which comprised the majority of my spell casts. The damage was decent at best, but Slow was incredibly invaluable when you run outlands heroics with only a 4-man guild. I could poly one target and then kite another mob around all day. :P

Back to the OPs question...

During this time, I recall fire being the highest DPS, but frost was preferred for raids because the mana regen to the group was too good to go without. Fire was pretty easy to manage. Get Improved Scorch, stack it 5 times, then lay into the target with fireballs. Use PoM-AP-Pyro to start before the fireball barrage, if you want to maximize DPS. Refresh a scorch every 12 seconds or so (think the stack had a 15sec timer?) so the stack does not wear off.

Frost spec is usually built around the water elemental, which you need to pop, but had a fairly long cooldown back then. So every five minutes or so they could spike their damage for about 45 seconds. Damage was mostly frostbolts.