I ran 2 of my characters (tank and mage) through nexus with some guildies. Our first attempt at the dragon was miserable.
My mage ran out of mana and did around 450dps
The second attempt I changed my castsequence to nothing but instant cast spells.
Mana was no longer an issue and my dps jumped to almost 900. but tanking and dps'ing makes things a little more important to focus on the tank.