Though I have 7.1, I'm not in the "you have to have 7.1" camp. I think it really depends on how many rows of seating and how far from the front/back wall they are.
If you're doing one row at 12-13 feet back, 5.1 should be more than adequate, especially with good di/bipoles on the sides to create a nice sweep of sound behind you. With only a couple of feet behind the seating, the sbl/sbr may really "scream" at you or become too point defined.
On the other hand, if your main row is at 9-10 feet, that would still leave 6-7 feet behind you, and the extra two channels would likely make a difference in filling it out, without screaming out their position too badly.
I don't know the totems that well, but a lot depends on the seating position and the speaker type used. Where is your seating going, and what do you plan on using for surrounds?
In my situation, I think it was worth it to go to 7.1 in my room, which is 18'x22', with my primary seating 11.5' from the screen wall, 9 feet from the rear wall (18" deep screen wall). I'm using all monopoles, the 6th and 7th channels really help solidify the rear soundstage. That being said it may change, as I will be adding a second row of seating that will be about 4 feet from the back wall, and I'm still researching on how to approach this so that the rear row doesn't get just blasted by the 6th and 7th channels.
So my vote is..... I'm pleading the 5th until I get more information. :^)