I tested open world xp gains with regards to solo, raid, or party. I plan on 8 boxing eventually, but first want to solo level a mage. So I tested mob tagging as a means to get ahead in the starter zone. I dont recall the exact numbers, but I specifically remember receiving more xp in an 8 man raid compared with my 5 man party. I was surprised by this as it was not the outcome I expected. If I had to guess at the numbers I would say it was something like 60 xp for solo, 25 for duo, 30 for 5 man party and 35 for 8 man raid. It could be that this wouldnt hold up inside a dungeon or it could be that Im completely wrong about what I remember, but if you could get roughly half normal xp in a raid it would seem like a good way to level big groups. Definitely worth further investigation.