This past week I decided to spend some time leveling my mage, so I could have another 85. The first time I did BRC at level 80 with several green upgrades, my damage was still pretty high at about 5k dps overall. I say this is high because when my druid hit 85, she struggled to hit 5k dps in heroics initially. After some gear upgrades and tweaking my rotation she did a lot better. I still hate my dps on trash though.
I mentioned this in guild chat, and several of my guildies were all, "Oh just wait until you get a level or two. Your dps will go down." A couple days ago after hitting 82 and having a good amount of blues (from the first BRC run and from tailoring as well as quests), I did BRC again and I did even more dps. almost 7k overall, and there were a few times where I hit 10k dps. My eyes just about popped out of my head.
I've been browsing through the stickies, and I see that arcane damage goes down once you hit 85, but ****... it's freaking crazy right now. And the slow added to Arcane Blast via talents is freaking awesome.