FlyingforFun,
The procedures you are flying will likely be designed for Cat A & B aircraft at least if not for A, B, C & D. In terms of procedure turns, if Cat B, C or D aircraft are allowed to use the procedure then the protected area will cover the highest speed that can be used. So you could in theory wizz around the procedure turn in your Duchess at 200 knots and still be OK.
As a further explanation - I previously flew for a turboprop operator. When operating into big airports with procedures designed to be used by any aircraft we could complete the initial approach at any speed we liked. We just need to be sure that we were at the appropriate speed for our category (B) for the final approach. But, when we flew into small regional airports, some of the procedures were authorised for use by A & B aircraft ONLY. This would usually be expicitly stated on the appraoch plate or you would simply realise that only Cat A and Cat B minima were published. We then had to ensure we flew the procedure turns at a max of 140 knots.
But if the entire procedure is designed for Cat A only, then you are correct. You can not fly the procedure turn at 120 knots. If only Cat A minima are published for the approach, then this is the case.