When I had a quad monitor setup (All CRT's), I used a mouse, but I mainly spent time on one screen. I probably cranked up the acceleration, so that I could "Flick" it over to another screen when I needed.
That said, I'd definitely go with a trackball. I have a CST PC-track, and it's great. I imagine you want the 1600 DPI L-track X. Or the 3200 DPI if you can find it. As an added bonus, it'll look boss next to that topre.