In this video Dr. Peter Attia gives a testimony about his transition to low carb eating, some of the reasoning behind it, and how it effects his mental and physical performance.
I've also felt the mental effects that he describes around focus, but that was mostly in a fasting state (e.g. ketosis brought on through starvation). Likewise with physical performance (fasted for 24 hours and played intense basketball with no negative side-effects).
Have you felt either the physical or mental benefits of being in deep ketosis?