I think practical experience (and Charlie has had plenty of that … all in the line of duty of course) drinking beer suggests a little is good but too much is not. How much is too much will vary with the individual. But there are abundant stories of how a beer or two can help.
According to Caribbean sprinter of the 1950s, Mike Agostini, the first 46sec run for 440yds by Herb McKenley was run when he (Herb) was still drunk. (that may have been sub-46, don’t have my “progressive world records” books with me right now.
Also I spoke to Chava Sobrino, the Mexican coach of the only non Chinese diving gold medallist at the Beijing Olympics and he said he once took a diver out for a beer the night before the major comp of the year (not Beijing) because the kid was a nervous wreck and wouldn’t have got to sleep the night before diving the following day. “What would you rather work with: a kid who had not slept, or a kid who might have his performance slightly under-par due to the effects of one beer?” was how he put it.
Trouble is for most footballers (why is it nearly always footballers) one beer is good, but they rarely stop at just one.