Straight-in approach speeds would be used; meaning your aircraft approach speed for a given weight/configuration would have to be below 140 knots to execute the straight-in maneuver and remain within CAT C minima. For example, a Learjet 60 would be a CAT C aircraft on a straight-in approach, and a CAT D aircraft when circling (vRef +10 put you at 145-149 knots, depending on weight).

You ask a very good question, this came up all the time during our Aspen training sessions at FlightSafety Atlanta in the LR60.