Thanks Mike for your question. You are right in your calculations. Normally FREE package(
http://appwarp.shephertz.com/pricing/) of AppWarp is suffieicent for multiplayer games with good number of active players. There are multiple benefits of message based pricing, there is no limit of CCUs, DAU or MAU which means you don't have to go to higher packages in case of CCU spike. There is no restriction on players/room or message/room.
Though looking at your game's play it seems CCU based pricing suits best in your case. We do give CCU pricing on requirement basis. I have sent you an email with the details of CCU based pricing.
Also as per your calculations you are sending 80000/(5*60) = 267 secs approximately. This is quiet high for a 2 player game. You can separately contact support@shephertz.com to help you optimize the number of messages being sent per second.