I love it when chicken owners realize Silkies should not be mixed with LF.  I would not mix Silkies with any other breed over 5-lbs and must have gentle temperaments.  The best breeds to get along with Silkies seem to be the under 5-lb crested/bearded/muffed/feather-footed fowl like Sultan, Polish, Araucana, EEs, Ameraucana, Breda, Cochins, Houdan, Faverolles, etc which are basically non-combative breeds as well.  Crevies are crested but are larger and a bit more independent and wilder in nature so don't think they'd fit.  The only other non-crested LF I would mix with Silkies is possibly Dominiques since those hens usually don't go past 5-lb and have a gentler nature than say a larger dual purpose BR or RIR.  IMO no LF roo should ever have access to a 2-lb Silkie hen.