I'm speaking from the mid level (End Game) - Not progression, not trapped in quest greens. So - I'm in mostly "Badge" Gear and 346 Heroics. I have Blue Gems, one or two Greens. Everything is enchanted - even if it's an Old Wrath Enchant. (Blackmagic is still easy for me with a 'chanter alt)
I'm not seeing this massive difference in DPS that people at high levels are seeing. If the RNG smile on me as a Fire - I can stack about 10k for my combustion. IF I'm super super lucky I can Spread combustion. But most time the RNG treats me like normal. I get about a 6-7k combustion and spreading it either doesn't happen or happens, but the other mobs die so quickly it doesn't matter.
In arcane I can /oom on trash pulls or the various "BIG" Trash mobs.... But if I just common sense and a little mana management - I'm usually easily doing 10k DPS.
So my findings:
Fire (Lucky with RNG) - 16 to 18k (Roughly 10% of the time)
Fire (Normal RNG) - 8-10k (Roughly 90% of the time)
Arcane (RNG is not an issue) - 10-11k (Roughly 100% of the time)
Frost is horribly lagging, but I have no idea how to FROST DPS - I'm Pulling 4.5k atm.
From a Damage perspective. On every fight my DPS rank is > my Damage Rank. But my damage rank is not terrbly lagging the others... It's usually about 120k maybe to 200k on most boss fights. (As I'm crit'ing for 40-55k - that's really not much more than a few shots...)