There is no set definition on stages. The higher up the stage will give you an idea of how stiff the clutch is, what shape the clutch disk is, and what the clutch disk is made out of. Personally, I think rating clutches in stages is retarded. What you should be concerned with is the clamping capacity of the clutch if whether that will work with your setup.

The HDSS is a great clutch and is rated for 243 ft/lbs of torque holding capacity. That will give you plenty of clamping force with a slightly increased pedal effort and the smooth engagement of a full surface street disk.