I've done the same with the Gamsat Scores for 2006 - again, they use a pretty weird scale so it's quite approximate in parts and I've rounded it all up so, if you don't see your score on it,
je suis désolé
The cutoff point this year for most GAMSAT unis was 63 (same as 2005). According to the graph, that's the top 28% (if they'd gone for 64, it would have only been 24%) so they seem to be sticking to the top 25% to get an interview theory.