Not to be completely cocky Mr-know-it-all here... but I have leveled a Mage (my third) who dinged 70 just as WoTLK was released. He was around level 55 when 3.0 came out.
Fire is, for all grinding intents and purposes, dead beyond 55 and quite possibly before with the introduction of 3.0. Sure you can use it, but you can use Holy to level a Paladin if you want. Fire's beauty lies in logistical benefits such as Blast Wave and Dragons Breath and its oddball defense mechanics including Fiery Payback and Blazing Speed. In high end fire stands simply to the benefit of Frostfire bolt, where a deep fire mixed with a mere 8 points into Frost allow for massive Frostfire critical strikes with the benefits of ignite - nothing to be scoffed at.
At precisely 60, Arcane jumps out in the realm of Grinding as one of your best options. Stacking ex-healer gear and utilizing Mage Armor along with proper glyphing will allow you about 280-300mp5 through casting at that level (nearly 700 at 80). Combine that with unstoppable Arcane Missiles + Slow + Arcane Barrage + Missile Barrage and factor in that the Arcane Tree now boosts stats like Demonology does for Warlocks and you'll find yourself with far higher stats than your fire and frost counterparts.
This is NOT to say that Frost is by any means dead, however. Frost will not have the automatic mana gains provided by Arcane, but really in all other aspects of gameplay it will surpass it. In the end, me and a friend who were very competitive leveled neck and neck with each other (I was Arcane and he was Frost) until I seemed to hit a brick wall in Dungeons at about level 77 and took the long road to figuring out FFB. He realized not much after that his high numbers in Instances were only from superior blizzard DPS and that on bosses he too was falling far behind on the meters. In the end, levels 75-80 are rough on a Mage, at least when you compare our damage with the likes of DKs, Hunters, Boomkins, etc.
Arcane's strength is to end a battle with Full HP and Full Mana, where Frost can only say it can do one of those things. Frost's ability to down monsters faster, however, generally equals out the Kills Per Hour to be near exact.
If you're Frost just Stack Spell Power. If you're Arcane stack Spell Power, Int, and Spirit - Healer gear XD.