While the following information is dependent on your battlegroup being good at PvP, this is by far the fastest way to get 8 levels. I am not sure about everyone else, but leveling the dreaded 50's always turned me off from making alts. I absolutely hated it on my first two characters and never wanted to do it again. Not anymore!
The method is very simple: Alterac Valley.
Yes that's right. Levels 50-58 are unbelievably easy to get in AV. A typical AV match lasts 20 minutes, and with a victory one normally gets 10 bars of EXP. To add onto the total, one can capture towers and assist in other objectives to boost that experience gain, but a simple win gets 10 bars.
Now this is all dependent on your side of the battle being good, but even with a loss you can get 4-5 bars of EXP, by capturing all the towers and killing the "Mini-Boss" of the opposing faction.
I have personally tried this and think it should be shared with everyone else.
I used to dread leveling because I knew I'd eventually hit 50 and bam it would be off to searing or Un'Goro and I hate those places. Not anymore. My big tip is to wait for the weekends to do this, when there are more people PvPing. It makes the queues much shorter.
Just this weekend I leveled my druid using AV. I got from 52-58 in just about 2 hours. I was in shock that Blizz would give away EXP like this.