This extract from a report of an NOAA trial gives more info:
"The vortex velocity of the 757 was approximately 50 percent higher than that of the 767 at similar vortex ages younger than 60 seconds. The most-intense 757 vortices were measured in the landing configuration with a flap setting of 25 to 30 degrees [tangential velocity of 326 fps]. The 767 vortices were longer lived than those of the 757, but were less intense than our baseline 727 aircraft [235 fps]. The highest 767 vortex was measured at 190 fps,"