There is a difference in the interpretation of the criteria:
TERPS CAT C: 140 kts max for final approach segment, based on Vref or (1.3Vso), and 140 kts max for circling.
PANS-OPS CAT C: 140 kts based on speed at threshold (Vat), 160 kts max for final approach segment, and 180 kts max for circling.
The aircraft manufacturer provides the airport reference and CAT specification, however, your airline SOP may modify this.
Airport Reference Code and Approach Speeds for Boeing Airplanes
Edit stuff: To the original post, the reference speeds are TAS. TERPS turns assume a MAX bank angle of 18 degrees.