Went out this afternoon with my iFlight Titan DC2 4S and I think I might have a new entry for the leaderboard…
36.34m/s, or 81.29mph 
Conditions were a light wind ( UAV Forecast reckoned about 13mph ) blowing from the East, so the speed runs were done from E to W. Not sure if just oldish batteries, or because it’s the first time they’ve been fully charged this year, but had pretty bad voltage sag ( down to 13V ) and they didn’t last very long at all - but they are just 0.450mah 
GPS speed data logged by Betaflight Blackbox, converted to .csv and .gpx using blackbox_decode.
Pic of the drone
Screenshot of gpx data dragged and dropped into Google Earth
Screenshot of the relevant .csv data
If anyone wishes to verify the data, the original Blackbox logfile is available at http://martins-models.co.uk/martin/BTFL_BLACKBOX_LOG_Titan_DC2_20220301_161317.BBL . The fastest run was on flight #2.
Interestingly, with a logging frequency of 500kHz the total of approx 8 minutes of flight today took up 6MB of Blackbox memory - handy as the FC in the DC2 only has 8MB available