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.