CPU 3960 I7 extreme edition ( overclocked through gaming profile which is 4.7)
Motherboard asus rampage iv Extreme
Sli Titan Hydrocopper 
power supply Evga Supernova Nex 1500
Ram 4x8gb = 32gb corsair Dominator 2400MHZ
and i have a good custom loop
 
first i want to know which tool do u guys use to overclock and i tried with msi after burner and i pushed like 100 first and when i tried i kept getting error TDR crashing the nvidia install so i thought maybe its about voltg but i have no experience in it so please help me if u can i want to know the safest voltg without doing any dmg to my cards and i want to push them as much as i can becuse am having difficulty at some games specially The Witcher
 
Thanks,
Much Appreciated,

well i have 4 of them in 4/way sli but still building them but should overclock the same way as my 780 ti's i would use precision x16 move evry thing to max thin start by move fre's us a little at a time to see how far your cards can go

i tried that but it kept crashing giving me TDR error whats the fix ? if its voltage wats the safest voltage ?