Reducing my effective room size

You don't mention the height of the ceiling, but if it's a standard 8-10 feet, I can't see why your PSBs wouldn't perform well in that room (provided you've got adequate power). Stratus Golds aren't exactly small (sonically speaking) speakers. Partitions shouldn't be necessary.

I agree that the short wall would be the way to go if you can make it work. Even still, the long wall should work pretty well.

I used to have my system setup in a room that was 17X40 with 14' cathedral ceilings (the builder called it a "Great Room"). Aesthetics (WAF) prevented me from placing the speakers on the short wall. Even on the long wall, I was able to move the speakers about 3 1/2 feet into the room and it sounded terrific. The only thing that I had to do was add a subwoofer to help pressurize the room. Otherwise, I thought that it was a great setup. No issues with reflections, standing waves, nodes, etc.

I'd also suggest the short wall. The drapes behind the speakers should be fine. Then some sort of quasi partition (like bookshelves) could be used for diffraction behind the listening position.

If it were me, I would find a way to convince my wife that actually adding a wall (maybe with french doors in the middle) was the answer. My room was 14' x 26' and I added a wall to make my audio room 14' x 20'. That left my wife a 14' x 6' foyer to decorate. You could put your wall in so that your audio room was 16' x 22' (minimum) and that would leave a decent dining area.

Before I changed my room, I experimented with my system by swapping the speakers back and forth from the long wall to the short wall. I preferred the short wall. With the speakers on the long wall, the only advantage was that your side walls are a great distance from the speakers. This basically takes away the "first reflection point" problem. This type of setup gives really great horizontal (left to right) imaging and separation. But, because you can't pull the speakers off the back wall much without them being right in your face, your image lacks depth, its not very three dimensional.
When I placed my speakers on the short wall and pulled them out about 6 feet from the rear wall, the music was much more 3D. (http://www.cardas.com/insights/index.html)