Another factor is whether or not you have a decent place for the extra 3 speakers if you end up getting the 5.1 system. In my computer room, the only place I could put the rear two speakers was on my ceiling, which became a pain with the cables. Although, I have to say, the surround sound...
Yoshi is cool. The coolest thing I have seen of his is Yoshi's Boxx.
http://www.techtv.com/screensavers/supergeek/story/0,24330,3381725,00.html
So cool...