Chris, I'd go with a percentage of bodyweight for the most reps. This would maximise the amount of time each person ( it should be men and woman ) were " on the bench " keeping the crowd at your contest and exposed to your supplement line for a greater period of time. The total number of impressions would be exponentially greater.
I'd also invest in a custom bench ( go to a metal fab shop ) have it covered in a material with your companies logo screened on it. Have two giant screens on each side of the stage perched high. Have a camera, they are so small now their weightless, suspended from the ceiling and shoot the competetor as they take their turn. When Finished, the camera shoots your logo as the MC gives the official count and announces the next contestant, you have two 10 or 15 foot adds which can be seen from everywhere. A local audio/video company could do it for next to nothing. When I was in school I worked in the banquets dept of a large hotel and we did stuff like that all the time.
You gotta get OnlyMe there as the MC.
The Beef