I think you should go with 22 feet length. It's a big benefit that it will save you time and money, but even if that weren't the case, you should still go with 22 feet. If you put the speakers on the short wall, you will really need to put good sound absorption at the first reflection points on the side walls. Also, the speakers should probably sit about 4 1/2 feet off the rear wall.
If you center the speakers on the long wall, you won't have a problem with side wall reflections but you will not have good depth in your soundstage because your speakers will have to be so close to the rear wall.
Go to
http://www.cardas.com/insights/index.html
and click on "Room Setup"
If you center the speakers on the long wall, you won't have a problem with side wall reflections but you will not have good depth in your soundstage because your speakers will have to be so close to the rear wall.
Go to
http://www.cardas.com/insights/index.html
and click on "Room Setup"