+1 for a question involving the movie Limitless. I have been searching for a "Limitless" food and/or supplement for some time now and my list includes all 3 of the foods/supplements you mention, although I take niacin indirectly in the form of Picamilon (a nootropic combination of niacin and GABA that penetrates the BBB).

I can never forget the day I reintroduced butter into my diet after going without it for years because I believed the lies that it was unhealthy - an hour or so after I consumed it with a meal it felt like everything made sense to me and everything was right with the world. I read articles about health and nutrition (my passion) for hours straight without a break that evening. For proof that butter improves mental functioning, see Seth Roberts' experience with it improving his ability to do arithmetic (others have reported similar effects, including myself, although not statistically like Roberts did): http://blog.sethroberts.net/2011/11/25/butter-and-arithmetic-how-much-butter/

100% cacao seems to improve my mood more than anything besides butter, and it seems to make my thinking clearer as well, although I am not sure if that translates to increased efficiency.

Within a short time after consuming any of the above 3 foods/supplements, it feels like a light is turned on in my brain, and I experience a warm fuzzy feeling in my brain, most likely from the increased blood flow (Picamilon and cacao are both known to increase blood flow to the brain, although I am not sure if butter does).

Also a product I tried a few times because my brother used it with success called SeaCure deserves mention here. Too bad it gave me so much mental energy that I couldn't fall asleep anymore so I had to stop taking it.

It is weird answering a question that I could swear was asked by me, but great question nonetheless.