GTAO (ground truth ambient occlusion)

https://developer.blender.org/D2845

If optimisation is the goal, you should check "Practical Realtime Strategies for Accurate Indirect Occlusion" and do what they do to reduce noise (2 pass bilateral upsampling, lower resolution AO computation etc, temporal smoothing).

http://c0de517e.blogspot.kr/2016/08/activision-siggraph-2016.html

https://github.com/GameTechDev/ASSAO/issues/6

http://blog.selfshadow.com/publications/s2016-shading-course/#course_content