Sorry, but the CAT does exactly relate to the final approach speed, the speed at threshold, depending on the criteria. For a procedure design, that CAT speed is used for the entire final approach segment, from the FAF on in. There are some differences between TERPS and PansOps, but for the designer, there is not, for example, under ICAO, you cannot use 160 kts for the final approach segment for CAT C. Likewise, with TERPS, you are not going to be circling to land a 738 at 140 kts...
While the tables and criteria claim differences, the design criteria is basically the same.
If there is a turn after the FA, the turn max speed is the CAT speed. If there is a turn that ends in the FAF, that CAT speed is used back to the beginning of the turn...
PansOps:
The following ICAO table indicates the specified IAS speed range, in knots, for each category of aircraft to be utilised whenb conducting the maneuver or approach phase specified. These speed ranges have been considered by the PANS-OPS approach designer when calculating airspace and obstacle clearance requirements for each segment of the procedure.
FAA TERPS is a bit different.
According to TERPS criteria, an aircraft shall normally fit into only one category. However, if it is necessary to maneuver at speeds in excess of the upper limit of a speed range for a category, the minimums for the next higher category should be used.
TERPS categorisation has identical speed ranges for the threshold speeds for each of the five categories, but the approach procedures designed under TERPS do not consider the circling speeds
TERPS has a simple table for the final approach segment:
EDIT: Look at this from the programming and automation perspective. Since there is no speed restriction coded on threshold, how would you automate the ac going from 160 kts on final to a max of 140 kts over the threshold? In the programming, it is per segment in the coding in the FMS, the ac knows that at the FAF, I am a Cat D, and will manage the speed to meet that target. When you are on auto, are you placing speed restrictions on threshold, or at the FAF, or does the ac manage that?
Assuming Australia operates to PANS-OPS, it's got nothing to do with final approach speed. The speed that determines the category is Vat, which is normally 1.3Vs. Our "approach" speed is Vat+5kts (not 737 but "normal" big jet ops, I suspect).
so Vat+5kts, the 738 is not exceeding 140Kts at threshold? That would take a bit of intervention...