Ok so this will guarantee getting the world/realm first 85 in 20 minutes but requires alot of saving up.
(Try to get people from your guild to help! Keep in mind this is alot of Saving Up!)
You are going to need: Sealed Vial of Poison - Item - World of Warcraft
These give around 20k EXP Each. You need to save these up and get around 300 or so (I think) before Cataclysm comes out. You get them from fishing dailies, and can buy them off the AH. This is a pretty big job to do, but if your really determined to get to world first 85 in the shortest time once the expansion comes out, this is most likely the way!
Just a Reminder - If your going to post things such as "Doesn't help me i won't do it" "OMG Lame too much time" Please don't post at all. Thanks!