I'm making a significant push for first 85 priest. Usually first 85 raw is done as a team. I predict about 3.5-4 hours a level.
1)
Starting Zone - Start in Mt Hyjal, Vashjir is beautiful but underwater is slow even with the "benefits" you get early on. Also the pacing of the zone is significantly slower than hyjal, a lot of "gather stuff on the ground" quests. I don't think anyone who starts in vashjir will have a chance.
2)
Solo - No grouping, you cannot afford to lose kill xp, only group up to do a roadblock quest where you could be potentially waiting for spawns. This is going to be a cutthroat world though, if you're first to tag something in front of another one of your class, you don't want to give up any ground, taht's 2-3 minutes they will be behind you =p
3)
Questing -The big debate is dungeon grinding VS quest grinding. IMO dungeon grinding will not work because even the normals are pretty tough and long to clear. No more mass AE, and a wipe is devistating. But mob xp in dungeons is pretty high so potentially a supergroup familiar with all the zones may be able to pull this off. I would hazard a guess that doing dungeons at all would be counterproductive.
4)
Ignore the Lore -To realistically have a chance at realm first 85, you can't enjoy the lore on your first playthrough. An instant quest turn in is a must, there can't be any downtime whatsoever. I currently have 200 swiftness potions, 200 mana potions, 10 swim speed potions, 10 water walking potions (this probably wont matter), 40 fish feasts, 25 flasks, 6 eternium thread (tailoring enchants) 4 boot enchants for run speed, and 2 of every 2nd teir enchant for newer gear. There are a lot of caves in cata, so swiftness potions may help avoid a wipe or get ahead of people in roadblock quests.
5)
Access to mages - This is going to be extremely important, at hitting level 82 and 84 you will be in kalimdor and need to be able to get back to stormwind asap, and you shoudln't leave your bind there. It's more efficient to bind as you go in questing zones and use your hearth as a quick way to turn in quests once every half hour. I don't beleive there's a stormwind portal from Hyjal or Uldum, so it will be very important to have access to a mage FAST to get you back and questing again.
6)
Inscription - Someone needs to level up inscription, there is a very early on item called Adventurer's Journal
http://www.wowhead.com/item=62237. It has a 1 hour effect and a 4 hour cooldown. 1 of the effects is 10% additional quest exp, this is one of those lucky moments that can turn the tide in a grind to 85, you'll realistically have about 6 chances to get this. The other effects are nice as well, bonus damage to things and a movement speed bonus. It would take too long for a person trying for 85 to skill this up, so it would be nice if a guild inscriber got this fast and was able to supply the books
7)
Guild Levels - Not much we can do about this proactively but it will be important as high population guilds will probably have an advantage. Guild rank 1 is 5% exp bonus to monsters/quests. Rank 2 is a movement bonus, and rank 5 is a 10% bonus to xp/quests, Rank 7 is 15 minute hearthstone. A guild that can get to level 5 fast will have a remarkable advantage, but noone really knows how fast guild leveling will work as it was quickened in beta.
8)
Sleep Deprivation - If you plan on going to bed, don't bother. The first 85's will happen under 20 hours of playtime so the psycho through-the-night grinders will beat you for sure.
9)
25/25 dailies - I'm actually doing this but i'm not totally sold. I'd almost rather get a head start in hyjal, but the exp from this is too significant to avoid. Have 25 dailies ready to turn in at 12:01. I currently have 25 in icecrown and dalaran, including the raid weekly which will be worth 2 dailies. I plan on starting on the skybreaker, flying to shadow hold, tabarding to tournament, ringing to dalaran and hearthing to stormwind prior to going to hyjal.
10)
Intangibles - Beta was full of buggy progression killing quests, especially in uldum. In Uldum there was a bugged quest that blocked 80 of the quests in the zone. It appears to be fixed now, but being the first person in these zones will probably not hurt as the quest usually bugs as more people try it and mess it up.
11)
Know your Class Benefits - Remember that you are competing against your own class, so don't be forgetting to use something that someone else could be taking advantage of, such as shamans with their quick hearthing, this is a remarkably fast way to turn in quests as most hubs have an innkeeper. Paladins should never forget crusader aura, etc. If your leveling spec has a movement speed talent, it will almost certaintly be worthwhile to pick it up, usually you can sacrifice something that won't hurt your kill speed enough to counterbalance it.
12)
310% speed - If you do not have this right away, the odds are strongly against you, over the course of 20 hours you will simply lose too much time travelling.
I've been planning this for a while and win or lose it'll be a geeky good time. This will not be the most fun way to get through cata obviously, there are hundreds of beautifully scripted events and fantastic storylines that shouldn't be missed, but for the topic it's important to just move on as fast as possible. I predict the realm first 85 will probably be about 13-15 hours in, cause usually crazy people level up as a team. I predict my own level 85 to be at around 18-19 hours and I'm just hoping no other priest is as insane as i am.
Delnar/Terry