I've been lucky enough to see WRs and been at the World Championships.
but one performance that sticks out in my mind was Butch Reynolds running a 400m race at the old Roggy Invitational on june 11th 1992, at a high school track in New Jersey, i don't know if its the best, but its the one that still gives me chills:
Reynolds had been banned by IAAF, and was fighting a battle to get his name cleared. he was waiting on a hearing that would take place a week later, but needed a qualifying time for U.S. Olympic Trials. the window was closing fast on his olympic dreams. The IAAF came out with an order initially saying that anyone competing in the same meet as Reynolds would suffer a ban too. They then back off a bit but said that anyone who was in the race would be banned.
there was major speculation about who would take the track with him - if anyone. the meet was actually a good one at the time - guys like roger kingdom, charles austin, eamonn coughlin competed there.
in the end, guys like miler charlie marsalla, and a few local club guys got in the race. the stadium was jammed packed - they drew something like 4,000 people that night.
reynold ran like a man possessed - he hadn't competed in a long time. he looked like he was fueled soley by rage against the IAAF. he was out like a bat out of hell, and just tore up the track.
44.67
on a high school track. in front of thousands. in defiance of the IAAF. no one was banned. reynolds won his case. won gold in barcelona.