Best word processor in regards to battery life?

Hello! I bought a new MacBook Air 13" (Late 2010) recently because I wanted something that was ultra portable and could function almost solely as a word processing machine. Anyway, the question is, based on battery life alone, what is the best word processing software for OSX (10.6.4)? By "best" I strictly mean what will let me have the program constantly running and drain the battery the slowest?

Obviously it seems like a choice between Word:Mac 2011 or iWork Pages 2009. I'd just like to have the program run in fullscreen mode and leave it like that for as long as possible, closing the lid when I'm finished writing and then opening it again to find my work exactly as I left it WITHOUT my battery being at ~6%. =)

So, anyone have some experience with what I'm trying to ask? (This is my first Apple machine ever so I apologize if I'm asking some obvious questions, I'm pretty oblivious to all things OSX.)

Thanks!