First thing is what will you use it for? gaming (performance) or business/web (functionality)???
You will only need a 7990 for gaming performance, otherwise a 7870 eyefinity 6 edition will be enough.
http://www.powercolor.com/Global/produc ... asp?id=415(just an example of a 7870 e6 card)
You can crossfire this with another 7870 NON eyefinity 6 card for more performance (4gb total VRAM)
The reason is that WHEN CROSSFIRING THE OUTPUTS ON THE SECOND CARD ARE DISABLED (sorry for the caps but I found out the expensive way.... (Also there are micro stutter issues in some games with xfire)
The 7990 will need a Club3D MST (multi stream transport) hub to run 6 monitors
http://www.ocaholic.ch/modules/smartsec ... ng=englishI do not know where to get these but a few ppl here have purchased from amazon/germany...
BUT to run them together as a single display (Eyefinity) you need to run the same res (2560x1440 per screen)
The 7870 e6 will do this as display port will support up to UHD (4k by 2k) per displayYOU WILL NEED A MINIMUM OF 4 ACTIVE MINI DP > DVI ADAPTERS FOR THIS TO WORK
(Unless the displays have display port inputs)
Another card which you could consider is the Asus 7970 DC2 top
http://www.asus.com/Graphics_Cards/HD7970DC2T3GD5/BUT you will only be able to do 1920x1080 as one output is DVI-D and the other DVI-I (This card goes in to 6 monitor mode when u switch the onboard BIOS to the other position im pretty sure...)
PS: Im not sure if you want to run eyefinity....? But still the 7870 e6 will power all these displays, say a 2x2 group plus 2 extra sceens? Is this what your aiming for? (And u can still xfire for more grunt...)
EDIT: (This shows the possible eyefinity configurations)
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