To answer your original question I think we'd really have to perform a very specific case study that would require a control and variable in order to deduce the correct answer mathematically speaking of course. I would spend some days giving every closer coffee for the whole day maybe around 2,000mg a day while other days I would give decaf, say its regular coffee, and see how productivity for all closers functioned that day. I would compare the productivity of your best closer to your weakest closer and see how far the separation was in performance. Now this is where things would get tricky. I would then give your good closers regular coffee maybe 1,000-15,000mg a day and your bad closers I would continue to give them decaf while telling them they are getting regular coffee. Then I would compare those numbers again to the performance of previous numbers and to compare the good closers to the bad closers. I would lastly give decaf to the good closers and regular to the bad closers and once again see the ratio between closed deals compared to non closed deals in previous case studies while also seeing if the good closers took a dip in closed deals that measured simultaneously with the improvement the bad closers had that day.

I think that would be the only real way to scientifically find out if coffee should be given to bad closers