Probably not my place, as I am a relatively low end player compared to some of these guys, but I had put some thought into this, and I came to the conclusion that a 5v5, with all people you know of equal, or similar skill and constant ganks on mid would be one of the best shows of skills.
Also a best of 5, 1 playing against someone who counters you, one playing against someone who you counter, 2 alternating first picks, and a tie breaker in however you prefer. This shows how people capitalize on a clear cut advantage, how people handle a clear cut disadvantage, how people pick when given freedom and knowledge of what the enemy will pick, and a tie breaker up to the discression of the main player.
This is how I planned to recruit people, but I'm still a few months off from being good enough to try to be serious on this game. Best of luck to you recruiting, and I personally think your current method is pretty terrible. :x