According to my company's SOPs:
For Boeing 777 (Cat. D):
Normal taxi speed = 20 kts
Taxi during turn = max. 10 kts
Maximum taxi speed on straight taxiways = 30 kts.
We had exactly this question in my last sim-check, and the instructor told us that, in a high-speed taxiway, the maximum taxi speed of the aircraft applies.
So in case of a 777, that would be 30 knots.
Likewise for any other aircraft type (according to my airline), it would be whatever is written in the FCOM chapter "Limitations".
I doubt whether any aircraft should vacate the runway at 93 km/h, because it would mean that part of your landing is still on a taxiway. Another sentence in the OM-A says that the aircraft should reach taxi-speed before turning off the runway.
So I think the answer to the question is: the aircraft's maximum taxi speed.