The fastest declared task with thermals in history: 205.98km/h.
My father and I flew this African Continental Record in 2015 (100km FAI triangle speed). I remember this flight vividly. The thrill and excitement during the attempt and crossing the finish line were a once in a lifetime experience.
This task took a lot of preparation, but the final plan was rather simple (but a lot of attention to detail was necessary). It was carried out exactly like planned, and succeeded on the first flight.
The forecast that it would be quickly superseded did not take place up till now, though. Until this day it remains the only declared task using thermals that has broken through the 200kph barrier.