In response to your last paragraph, I don't think there is any advantage, in fact I would suspect the opposite. One thing to consider, given the width of your room, is to try setting up your speakers on the long wall - that should pretty much take your horn shapped 'side wall' out of the issue. Personally I've never cared for the sound of long wall set ups, but a lot of folks really like it.
As you say, try them all, that is really the only way you will know.
As you say, try them all, that is really the only way you will know.