Well at the moment its a temporary storage anyway so its more just for fun.....
But what I could do is determine a score based on the number of players in each race, and the streak with the highest sum of these points is regarded the top streak.
I could just make it so each player is equal to a point.
So say on race one there were 14 racers, thats 14 points. next race there was 8 players, so a total of 22 points, then gets beaten.
At that stage could say the best streak is 2, beating a total of 20 racers along the way.
A better streak would be one race with 24 people in it, or two races with 12 people in them etc etc.