I remember the Boeing training document, about taxi speeds and tyre heating, mentioned by Kenparry. It contained a graph which illustrated the amount of heat that was going into the tyres Vs taxi speed, due to tyre hysteresis. I was fairly linear up to about 20kts, then went semi-exponential through the 25-30kts range and upwards. The message, as I remember it, was that a MTOW 'heavy' which was taxiied at 25kts for 5Km in 25-30 degrees ( very possible at a number of Middle East airfields) was going to be near tyre fuse-plug failure nearing the end of 2Km+ takeoff run. The main issue was tyre carcase heating. 20kts, briefly 25kts was recommended for taxy. If tyres are designed to handle speeds of around 150kts and heavy braking on runways and 40kts on high speed turn-offs, taxiing at ANY speed, short of getting airborne, is possible for short periods. Safety and common sense dictate otherwise and most company flight manuals give recommended taxi speeds in the 20-25kt range ( maximum figures, good conditions, etc)