Overclocking will help a bit, but you're still likely to run into slowdowns on occasion. The GTX 960 may also have issues running games on ultra, partly due to not having quite enough grunt for some titles, and partly due to VRAM limitations. A number of newer titles need 3 to 4GB of VRAM to do ultra, even at sub 1080p resolutions, and unless you're going to splash out a little extra to get a 4GB version of the GTX 960, that might be an issue for some games. It's why a GTX 970 or better is usually recommended if you want to go for ultra.