There's a reason bantams are usually sold unsexed (straight run). They're very difficult to vent sex (vent sexing experts don't even try), but maybe some bantam experts will pipe in with other telltale signs of gender in bantams.
I have several bantams and would totally agree. They are just 6 weeks and their is definately a difference. Red, larger combs and the Waddles are definately bigger on the Roos. One or two, I am not real sure. Good Luck and passing on patience as you wait.