We have never had a silkie or cochin bantam go broody, ever. We have had lots of wyandotte bantams go broody, the phoenix bantams, and the OEGB hens are all good broodies.
I agree with Silkies, all 5 of mine are broody...although...I have a Black Jap and 2 Mille Fleur d'Uccles that are also broody. My OEGBs aren't old enough yet to know how broody they get.