Not this again
30-40%
980 OC vs 980Ti OC and the Ti is a good 30-40% ahead, they are super quick cards.
Both 980 and 980Ti also both overclock extremely well. The custom 980 and 980Ti offered big performance boost over reference 980 and 980Ti, typically 20% faster out the box compared to reference versions.
Lets remember 980Ti reference was 1075MHz boost, yet custom cards were 1200-1400MHz region and pretty much every 980Ti could OC beyond 1400MHz with some even over 1500MHz. The 980Ti in particular gained huge performance from the OC, it is one of the best overclocking cards of all time when nearly an additional 40% performance comes from OC alone. The 980 was also very similar in such ability.