3 Monitor setups will ONLY work under windows 7 and allegedly vista too. (2 monitors max under XP)
I'm using an ati hd6950 which runs WOW @ 60fps quite happily (however it covers a full 3 Motherboard slots)
(The 5040X1050 option will not appear in WOW's video options till your desktop resolution has been set to this res.
Remember also that 5040x1050 is only used for 16:10 monitors & not the newer 16:9!!!!!!!!!)
All 3 monitors have to be identical to use the bezel compensation.
you will also need an ACTIVE display port to Dvi adaptor (around £27)
I havent managed to get Full Screen using DX11 (only DX9)
I bought a Superb quality 3 monitor stand for <£100 from Novatach (nice people gave me free delivery)
hope this helps.