I kind of agree with Eternad. I guess visibility shouldn't immediately be equated with the number of posts per week or the number of participants. There are other factors for a post, and therefore the signature, to be more visible than another.
True, but how exactly to measure quantify quality of members, amount of posts, places where those posts are written etc? Its an impossible task imho and what OP did is the 2nd best thing.
With over $6,000 weekly budget of stake, they can employ more than 60 participants and make a flat rate of $100 per participants. You can make the required posts per week to be 30 and then 15 of the 30 posts should come from the gambling boards. With this method their campaign will still have obe of the highest visibility in the gambling section while maintaining sanity and some more exceptional members of the forum could join their campaign.
Times where $100 per week could get you a top quality members are long gone as there's more spots in signature campaigns than there are quality members meaning even subpar posters can get into a pretty decent campaign.