HRC fork springs for the MC21 are part# 51402-NH3-761 rated at 0.6-0.85 kgf/mm & 51403-NH3-761 rated at 0.7-0.9 kgf/mm, and for the MC28 are part# 51401-NKD-970 rated at 0.95 kgf/mm. The fork springs are NOT interchangeable between MC21 and MC28.
I would use that as a starting point and say that street settings are marginally softer than that.