You will always split the XP with the rest of the group however, a full group (4, 5 or 6 player) will get an XP bonus to every kill which will offset the "loss" of XP to each player. In addition, a good group can always kill more mobs than a solo player. When a full group is clicking, they can usually kill non-stop with one or two DPS class characters pulling mobs back to the camp (in rotation) and the tank pulling aggro as the mob reaches the group.
Also remember that you get a (stacking) bonus for each player that mentors you and if you have "vit" you are earning double XP anyway. On top of all that, there are bonus potions for XP and crafting to make things go even faster.
Put it all together and you can almost hit the level cap before you roll up the toon!