From what I've read because of the change in the damage output to increased haste it ends up being about the same or actually a little bit better (haste is a really good dps stat for arcane, but it has negatives in that it means you burn through mana faster).
The issue is that you will probably want a more conservative conservation-phase rotation of something like AB2AM/Abar to make sure that you don't dip too low. At our current mana levels with glyphed mage armor our mana stays pretty high, but at 85 it will be quite different.
edit: here are the 4.03 changes:
Edited, Nov 24th 2010 10:32am by Anobix
Mage (Forums / Cataclysm Talent Calculator / Beta Skills/Talents)
Arcane Blast now increases damage of the next Arcane Blast by 10% per stack, down from 20%, reduces cast time by 0.1 seconds per stack, and increases the mana cost by 150%, down from 175%. In addition, the base cast time of Arcane Blast has been lowered to 2.35 seconds.
Arcane Explosion now costs 15% of base mana, down from 18%.
Arcane Missiles damage has been increased by 5%.
PvP set 4-piece bonus changed to increase damage by 5% instead of providing 5% Haste.
Arcane Barrage damage has been increased by 5% and its cooldown is now 4 seconds, down from 5 seconds.
Arcane Concentration: Now has a much higher chance (13/27/40%) of entering a Clearcasting state. This effect cannot occur more than once every 15 seconds. The tooltip still states that there is a 3/6/10% chance, as it averages out to approximately the same chance with the internal cooldown applied.
Arcane Specialization again increases arcane damage by 25%.
Blazing Speed no longer dispels movement slowing effects (it still dispels effects that totally stop movement).
Fire Specialization again increases periodic fire damage effects by 25%.
Molten Shields now also causes Blazing Speed to dispel movement slowing effects in addition to its current functionality.
Pyroblast base mana cost is now 17%, down from 22%.
Deep Freeze: the cooldown on this ability is no longer reduced by Haste.
Early Frost now reduces Frostbolt cast time by 0.3/0.6 seconds, down from 0.35/0.70 seconds.
Fingers of Frost proc chance is now 7/14/20%, down from 10/20/30%.
Frost Specialization again increases all damage against frozen target by 25%.
Reactive Barrier is now triggered by any damage which causes the mage's health to be below 50%, even if the mage was already below 50%.
Shatter now also increases Frostbolt damage by 10/20% against frozen targets.
Shattered Barrier duration is now 2/4 seconds, down from 3/6 seconds.
Glyph of Evocation now heals for 40%, down from 60%.
Glyph of Deep Freeze now increases damage done by Deep Freeze by 20% (no longer increases Frostbolt damage against Deep Frozen targets).
Improved Polymorph now correctly shares diminishing returns with controlled stuns.