I was running Alterac Valleys, avg. 4% per win at 88-90... 3.5% for LOSS and arround 5.5-6% for WIN.
AVG. it took me 5-6 minutes to enter and finish AV, either win or loss, so aprox 10-11 AV's per hour, which rougly means, you will need aprox 2.5 hours to level up from 87 - 88 - 89...
Seems like really good EXP per time invested...