I can see that many estimates on the speed of UA175 have been produced.
Knowing the skyline of NY and the spots from where the few available video were taken, isn't it possible, probably by using goggle earth and some basic trigonometry, to produce one more estimate that could confirm or not what has been published already ?
NTSB Video Impact Speed Study (8mb pdf)
Summary
Using distances taken directly from the video screen, flight 175's groundspeed was calculated to be between 473 and 477 Knots just prior to the collision with the building. Using distances taken from video screen prints, groundspeed at impact of 504 Knots and 507 Knots were calculated. This compares to an impact speed of 510 Knots calculated from radar data in the Radar Data Impact Speed Study (AA11 & UA 175)
NTSB
Radar Data Impact Speed Study (9.15mb pdf)
Keep in mind that the aircraft which impacted the south tower had mostly a headwind on it's path. So KTAS is actually a few knots higher than the groundspeeds reported above.