After reading dozens of forums and conflicting accounts, it occurred to me that lots of people here probably have this set up already

My PC's need an upgrade. I'm tired of managing so many desktops, so I figured I might give a software boxing a try. I've read there are all sorts of issues with multi-monitor support. Is there a major difference/advantage between SLI and CrossfireX that makes one better than the other for running 3+ monitors on dual GPU's?