So far, I have to admit, it's been far less hassle than I thought it would, apart from that HDMI issue which took me several hours to work out.
A little more searching and it seems like connecting 3 displays to one GPU works just fine if you only have one GPU....
If you have SLI, it will simply force you to connect one screen to 2nd GPU. What the hell is that about?
Does not seem there is any reliable way of switching between single spanned display and 3 separate screens - again, there are solutions with single GPU, but not with SLI.
So much for Nvidia drivers being superior!
Some of this stuff seems like it really shouldn't be too hard to do...