I'll throw up an idea that sort of blends some of the ones already suggested. What my clan used to do, since we had a large group of members, was split our active squad into two teams (red & blue). The teams were divided so that all members agreed that the skill level was balanced on each side (what we're trying to do here). Each week, the two squads would hold a scrimmage against each other; the winning squad got to play in the league match representing our team. It was a fair method that all our members accepted; everyone had an equal opportunity of being the "Gold" team for the week.
Also, I'm still confused on the tournament structure, but as far as teams are concerned, I believe we should continue doing what Frost has set forth. Let's continue dividing the server up as best as possible so that most, if not all, can agree on the skill balance and fairness of each team.
If we do want to have an "Optimal" team represent the Gold Rush Server, have each GR team scrimmage against each other. Whichever GR team wins is essentially the "Optimal" team for the GR server.
Personally, I don't mind if I'm on the A team or the C team, but I'm worried that there may be some participants or regulars that are concerned if they make the cut for the "Gold" team. What made a lot of members unhappy in my clan (and a few quit), was when we ultimately made a set-"Gold" squad.
Like I said, just an idea.