Board Thread:General Discussion/@comment-24312042-20131219121129/@comment-3014241-20131219132903

16x (☆☆☆☆) → 8x (★☆☆☆) → 4x (★★☆☆) → 2x (★★★☆) → 1x (★★★★)

It's mostly for Rs though, SR with 4* are quite rare and there's none for UR yet.