Pushing out 2560x1440x5 @ 60fps is going to be tough even if Quad SLI'ing 690s (if thats even possible) - they dont scale after 2 cards very well http://www.slashgear.com/nvidia-geforce-gtx-680-benchmarked-in-quad-sli-23219787/
EDIT: Oops forgot only Radeons can do 5x1, current Geforce can only push 3x1
Itll draw a ton of power (around 300w) and get pretty hot (around 80C) under load - so theres that to consider - id stick them in its own room if possible - all the fans sound like a jet engine (my crossfired 6970s are in next spare bedroom - and it gets HOT in there when playing a game, luckily i can shut the door.
and having 5x27" monitors at around 60w each - they get pretty warm as well (at least my Crossover gets pretty warm at around 60% brightness)
As for the bezel thing - honestly you dont notice it too much when youre actually playing the game and you feel pretty immersed, if you use bezel compensation it lessens it out even more ( i just pretend im in a mech hah) -
the real problem comes from unoptimized UIs, more often than not games will have UIs pinned to the left/right corners - and on a surround setting it gets REALLY annoying - sometimes you can live with it..sometimes you cant - hopefully the people found at widescrengamingforum wil have a plug in for that particular game that will fix UIs (widescreenfixer.org)
Oh another potentially HUGE problem is microstutter - which rears its ugly head in SLI/Crossfire setups in some games (max payne 3, sleeping dogs) - some games its not too bad (Batman Arkham City)
Another problem i had was the Fisheye effect - which is prevalent in ALL 3D games using 1 camera for pov (which is all of them) - even 16:9 you can see it happening at the ends of the screen - you can lessen it by having the screens completely flat and not pointed towards you AND not looking directly at them (only using your peripheral vision) - if you use a projection system you can get warping software but im not sure they work for monitors..
TLDR my problem with eyefinity was
1) GPU power not quite there yet
3) Heat & Power & Noise
4) Sometimes funky UIs, the need for 3rd party fix tools
Dont get me wrong - most games did work in Eyefinity - maybe 1 out of 5 didnt work to a point where i choose to play in single monitor mode. I sold my 3x1920x1080 TN monitors and opted to get a 27" Korean IPS, and overall its better for me although sometimes i miss the immersiveness of games when eyefinity does work properly