The GP104 GPU is capable of providing a 1607MHz base clock. This base clock value closely matches the base clock value of a stock GTX 1080. However, the boost clock only goes up to 1683MHz on factory overclocking presets. But that doesnt mean you cannot overclock it even further!
Generally speaking, the 10xx series overclocks to the 1620-1700 range, most of mine like to sit around 1630 but one commonly gets up around 1720 without issue (all at ~70% PL)