@Thieliste, Same here, long wall. I personally prefer long wall placement. I find imaging and bass response often improves with such a layout. But again, absorption directly behind the listener is required to avoid comb filtering. Even if it's just a temporary item used only during listening sessions. Also, pulling the speakers well out (>3') from the wall behind them will help with clarity.
If using spikes, I suggest removing them while experimenting. Replace them when ideal positioning is established.
9' could be ideal, but don't be afraid to try wider. Especially with such available space from side walls. Just a slight tick of just a couple of degrees of toe in could easily compensate for the foreshortened distance of listener from loudspeakers. It might really open up the soundstage. Keep in mind the center of the woofer's relationships to the various boundaries. Experiment! Test recordings can speed up the process.
Good luck!