My room is simillar in dimension, I tried long wall and could never get things to integrate well. I quickly went back to short wall set up. I'm sure I suffer a bit in stage width but it is a much better sound overall.
Try it out though, you've got nothing to loose but a few hours of set up time and a sore back.
Try it out though, you've got nothing to loose but a few hours of set up time and a sore back.