I would say, very doubtful. People were boosting when the cap was 85, and at 90 with heroic gear, you'll blow through the dungeon. You can always do a trial pass and see how it feels if you want, before you start your RAF timers. Personally, I've done Halls of Lightning with the Jade Forest vendor gear on a fire mage at 87 or 88. I also used a bad aoe rotation (only arcane explosion), so it wasn't a case of skill. I think some of the bosses required a bit more focus, but not much.