Yessir! Sure are. But. It all depends wich 560ti that you are referring to.

Depends on if:
1) The game can use SLI.  Most can, to some degree or another, but many can't.  For example, two I'm playing at present are 'Alan Wake' and 'IL-2: Cliffs of Dover'.  Neither can use SLI, so I'm basically getting single-card performance from them.
 
2) The game needs more than the 1gb of ram common to the 560 Ti cards.  'Battlefield 3', I'm looking at you...if it needs more than that, you'll be seeing pretty bad performance as the cards need to swap out to system ram.
 
Often, the 560 Tis in SLI will be faster...but not always.  And sometimes MUCH slower.