Be careful about blanket statements about breeds. Some Rocks are decent layers and decent winter layers. Some are not that good of layers, and some are awful winter layers. Trust me.
Just my $.02 but different strains, even of the same variety, may vary greatly. Some have been pushed to be good, solid layers, while others? Not so much.
They all bear the breed name Rock. But, their composites are so very, very different in their foundational makeup.