Hey,
Back in the day, one of the good things about leveling with a group (3 players minimum) and doing instances was the additional bonus XP that all of you got for doing so. For some reason this hasn't been introduced to any private server I have played on, including this one. I think it's a pretty important part of the vanilla experience for us who enjoy getting through the grind with a friend or three.
Rate for group experience:
1/2 person group = 1.0, 3 pg = 1.166, 4 pg = 1.3, 5 pg = 1.4
1 person = 100xp
2 people = 50xp each
3 people = ~39xp each
4 people = ~33xp each
5 people = ~28xp each