You best bet is to set WideViewAspect=True and stretch the screen across all 3 monitors. I have run a 3+1 setup for several years now and I will tell you that each window you add will bring your framerates down. Ill give you an example.
I have an i7-4770 at 4.3ghz, 16gb RAM, AMD 7950 running 5760x1080 with the haswell igp running the 4th 1920x1080 monitor and I still struggle with framerates at big airports. I have traffic at 40 clouds at 60mi and everything else max with bloom and lens flare off. At JFK I average about 17 fps. If I add another window that drops to 14 fps.