Taxi Speed
The most important word is APPROPRIATE. There all sorts of considerations that affect "appropriate" including cabin crew, aircraft weight, surface conditions, congestion, taxiway width / camber, distance to taxi, carbon or steel brakes? So taxiing at anywhere from 5 knots to around 30 knots could be appropriate under varying circumstances. Turning off a cold, wet HST scares the hell out of me .... aircraft tyres are designed for going in straight lines and not around corners!
FCTM states: "The appropriate taxi speed depends on turn radius and surface
condition.Taxi speed should be closely monitored during taxi out, particularly when the
active runway is some distance from the departure gate. Normal taxi speed is
approximately 20 knots, adjusted for conditions. On long straight taxi routes,
speeds up to 30 knots are acceptable, however at speeds greater than 20 knots use
caution when using the nose wheel steering tiller to avoid overcontrolling the nose
wheels. When approaching a turn, speed should be slowed to an appropriate speed
for conditions. On a dry surface, use approximately 10 knots for turn angles
greater than those typically required for high speed runway turnoffs.
Note: High taxi speed combined with heavy gross weight and a long taxi distance
can result in tire sidewall overheating. At maximum weights with taxiing
distances greater than 4500 meters, use 20 knots as maximum taxi speed."