If you have not seen the landing page here then check it out because there is a heavy incentive for players to stick in the same guild (differences and conflicts aside) to reap massive rewards (as long as you can keep up on the lvls).

From what I understand if you are lvl 115 by the time the GMs award the prizes you will also earn the prize. The same goes for being lvl 50/70 so if you want free stuff keep that in mind if not a server wide guild join the guild you know is gonna win and keep up with them :P