can only have 3 at a time(2 dvis, 1 hdmi, 1 dp). generally i switch to the tv when i am watching a movie or playing a game. i also extend to the tv for watching videos while working.
most days i actually have eyefinity off, and just run 3x1 extended with the monitors. i never include the tv in eyefinity.
i am only using 1 card atm, and have another in an htpc in the bedroom i can add for xfire if necessary.