There are different standards of 4K (3840 x 2160 pixels or 4096 x 2160 pixels).
Realistically it's whether the theatre even has a 4K projector. Most digital projections are 2K (2048x1080) in cinemas. 4K adds a slight improvement on those screens, but the reality is that anything over 2K is really much of a muchness in terms of quality due to resolution of display mediums (projectors, screens, etc.), ideal viewing distances, and the ability of the human eye to resolve detail.
The guys at Sony did a test on an IMAX screen years ago and found that you physically couldn't distinguish certain resolutions after a point even on those big screens. Increased resolution is rapidly turning into a marketing gimmick. 4K is, for the foreseeable future, a practical limit -- and even that's not a massive improvement to the layperson over 2K.