I thought that this would be an easy question to answer, but so far I have not found a definitive source. On sol 214 in this list of Viking wind speeds, 25.9 m/sec (93.24 km/hr) was recorded.
I have seen second hand sources that claim a maximum for the Vikings of 30 m/sec (108 km/hr) achieved during a dust storm. The Pathfinder Lander recorded generally much lower wind speeds and a lower maximum. I have seen second hand sources that claim much higher wind speeds, up to several hundred kilometers per hour, but these have always been unreferenced. Perhaps these higher speeds were observed as the movement of weather systems as seen from orbit, or perhaps they have been calculated. Does anyone have a good reference on this topic?