How far will it go? We managed 1,335MHz core (1,420MHz boost) and 8,150MHz memory. The card sat at a rock-solid 1,500MHz actual core frequency during the overclocking tests. Handily, while the extra speed does cause the fans to spin faster and temperature to rise to 76°C, it remains reasonably quiet in the overclocked state.
It seems as if breaking through the 5,000-mark barrier is a step too far for the GTX 980 Ti GPU.
Pretty good going for an overclocked card, but such is the frequency uptick already in place from Zotac, that going much higher isn't feasible.
A note on coil whine. The sample exhibited below average coil whine during our battery of tests. Coil whine was a little higher when left to render a game overnight, but basing results on a sample of one, the whine is less of an issue on this card than others. Your mileage, of course, will vary.