This is easier to have negotiations is your Pact Bro/Sis is next to you or before you (this is pro of this system)
But there are 2 cons:
I think that in PBEMs is better to leave a gap between rapidly negotiating factions so they could negotiate by e-mail during that time and come to a conclusion till turn comes to 2nd player
Jumping back and forth on GMTs will make this game extremely slow and you will soon find yourselves uninterested badly..
Better to have slower negotiations than slower game!
DataAeolus's fac is CyCon