I also play portrait @ 3440x1920.
I love it for MMOs and FPS.
My EyeFinity part is runnning 3240x1920, I think you mean the same resolution? I found that Bezels are pretty annoying. Not sure if bezel correction from driver is useful at all because I kind of dislike having text or information under bezel area.
I've been thinking about moving to 3 portrait, what GPUs are you running?
All four displays are connected to single R9 280X.