DarkW0lf,
darkdeaver has some very accurate info. I personally use the four round method on this guide.
http://wlodb.com/topics/169

The draw back, as darkdeaver pointed out, is that if you are one of the attackers you get considerably less XP. My attacking fire would get 1/4-1/5 of what my water would get. When I step up my team (2xfire, 1xearth, 1xwater) so that one of the fires was support only and the earth attacked with one of the fires, the support fire would get 3-5 times the XP compared to when it was attacking.

Good luck,

Spoiler:

Level 156 fire
T4
90% of the laws are made because of 10% of the people.