Before anyone asks - yes there are archived copies of old addon versions both on our github repository and on several of the addon sites we use, and these will continue to be available after Cataclysm comes out, so you'll be able to get those old files if you really want them. I'm not going to bother making these more easily accessible unless you give me a very good reason. "I'm on a private server and I need them since we didn't upgrade to Cataclysm" is a BAD reason - and it's illegal.
Also note that power leveling is sometimes used to refer to paying someone else to level your character to cap as fast as possible (i.e. they power level for you); a distinction used by Blizzard is to refer to the paid leveling as "power leveling service." This behavior is against Blizzard's Terms of Service. Power leveling yourself, which this article covers, is perfectly acceptable.
So, the initial leveling process is probably the longest it has been in an expansion in a long time. My first play through, it took me about 12 hours to finish every single quest in every single zone. Needless to say, due to leveling 7 times, my last leveling was done by a ret pally and took me just over 8 hours and completed every quest in the Horde zones. There are a few tips I would like to give for leveling in BFA.
This is also the reason why when I read in WoW forums of people skipping guide sections, due to being too low level I'm not agree and start ranting about it: it'll be a mess syncronizing with the guide and I've seen many people complaining about missing quests or accusing the guide for being innacurate, but not realizing that was their fault since they're skipping and missing a lot of quest chain requirement. Of course this apply if you're following a guide, believe me, it's very frustrating when you remain stuck in a guide section due to the reasons I've mentioned, more than doing grey quests (but they allow to be perfectly in sync with the guide) and goiing here and there to get the pre-requisite quests.
In Legion, some of the dungeons include the Black Rook Hold, a max-level dungeon in Val’Sharah that once served as an elven fortress but has been corrupted by a malevolent force. If you decide to quest in Stormheim, you can also try to clear the Halls of Valor, which lets you take on the Vrykul God-King and vanquish the pure Val’kyr that are superior to those found in Northrend.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide