It all depends what you want to do/play i myself went from 1 27" to 3 27" monitors 2 are ips and the old one is a normal TN all asus monitors.
IPS monitors are alot better in color then TN ones and you can notice it instantly.
I got a 3 monitor setup for eyefinity but as i did notice not that many games have optimized for multi monitor setups.
only some new games etc are somehow good but i have not played in eyefinity for almost half a year as i dont seem it to be worth it atm, but will most likley be much better in the coming years.
And if you tend to play in nvidia surround or eyefinity you most likley need a xfire or sli gpu setup to be able to power them as it will be 5760x1080 with 3x 1080p monitors so it will take alot of...