Zotac has its own "firestorm" software for their cards. Not that it does anything the MSI doesnt, but as stated in small increments and with careful testing.
The zotac 560ti AMP im experimenting with atm, is set rather high in voltage from the factory, but i havent seen any stability issues with turning it down (not that it does much for the fan noise or heat). Normally thou, as you go up in frequency the signals gets a little fuzzy wich is countered by setting a higher voltage (short explanation).
On my card theres room for insane overclocking in the software (like 100-120% OC) But since im running it with factory cooler instead of aftermarket water cooling, theres no way i can get wery far past the factory OC (AMP cards are allready overclocked from factory)