The playing with Rawr that I've done this past week (see, not just slacking off!) tells me that at my gear level (check armour if you want to see what that is) the highest DPS spec for a single mage in a party or raid is Frostfire, followed quite closely by 18/0/53 frost which is my current spec. Fire lags behind by some way, until you have a second mage to keep up the relevant fire debuffs (which frost and frostfire don't rely on), at which point fire blasts ahead. Arcane is great for burst DPS, but terrible for mana efficiency.
That said, even if I *were* able to produce the numbers that Rawr suggests I'm still nowhere near competitive with the higher DPSers (Rafaar, Parzifal, Kyon in shadow form), which suggests that there's still some way to go before I can be competitive in raids.