Fellowship is the big one. You can
triple your exp rate with a constant vitality feed to the PL toons.
Full group bonus is extra exp per kill.
As of this update, groups now gain 20% to 80% "group bonus" experience for having two to five members.
Full, six-person, groups now see an additional bonus. Their experience is only divided five ways, yet they still gain the 80% "group bonus." For those who think in terms of pie charts, it amounts to a larger piece of a larger pie.
----------
Oct 12, 2010, an additional bonus for grouping with players rather than mercs was added:
- Added an additional experience bonus for grouping with other players. Mercenaries will not add this new bonus. Each additional player added to a group will add a higher bonus up to the group maximum. A group of six players will receive approximately 22% more experience per kill than a group made of three players and three mercenaries.
Adding outside DPS would be next. For 6-man group (tank/heal/cc/DPSx2/PLee) the first 2-3 outside DPS toons you add will roughly half your kill time, then you need to add 4-6 more DPS to half it again. Diminishing returns at like 12+ toons total though, because mobs start dropping so fast. Going beyond that even at a fast respawn camp is tricky. Respawn timer or pull distance/speed becomes the limiting factor. Maybe a custom pulling macro that keeps 5+ mobs in camp or multiple pullers that ignore Xtarget count and pull from different directions could support a bigger killing team.
Assuming you put your two top DPS toons in the exp group, none of the outside DPS should KS often. You could set some DPS (monk/bst/nec) to auto-feign via KA once per mob if needed.
Raz's setup of 4 DPS in the exp group is even better.
There are also some
100% exp bonus potions from a anniversary quest if you plan ahead for next year. /claim had a few free exp potions on my older accounts.
Raids cut exp rate to about 1/3 of normal. So you'd need a very, very high kill rate to justify using them.