The 780ti reference model cooler does the job, it doesn't run too warm or loud , the advantage with this cooler is that it blows hot air out the back of the card/pc, you can overclock a bit on these but the after market ones are the better choice for overclocking.
Aftermarket coolers, usually run quieter and more efficiently , thus cooling the card better which allow for higher overclocking, the only thing is is pushes the hot air into the case of the pc , which isnt a problem if you have adequate cooling on your case with decent airflow.
Some also have better capacitors and are built for upping the voltage and power target