The 780ti is just an overclocked 780.And 780 SC is just the Superclocked version(made by EVGA i think).
It has some higher core clocks and memory clocks(not that much higher than the reference design imho).
You'll see a bit of a performance boost compared to the normal 780,but nothing spectacular.
Rather than spending money on a non-reference design,you could just buy a 780 and overclock it yourself(or don't,it's powerful enough either way,
especially in SLI).
The only noticeable improvement of the SC version is the modified cooler.But if you have good airflow and some decent fans,you'll be alright