The 580 should be sufficient for everything else except for metro and crysis. in metro, don't turn on MSAA and advanced DOF. in crysis, leave AA off. you should be ok.
you'll get slightly higher fps since ur res is slightly lower. again, turn off antialiasing. if enthusiast is too laggy, turn down to gamer.
if the 580 can't get playable fps, then the 560 ti SLI probably won't be much higher. The SLI 560Ti's put out 30% more FPS then the single 580, and cost the exact same amount as a single 3gb card (Australia pricing)
EDIT: if u want absolute maxed out settings in all games though,
only 580 SLI will deliver in crysis and metro. putting 2 of the "Single" most powerful cards in the word together is definately going to be the fastest SLI solution, but you pay for that privilege