Cossack
The prob here is the difference between the wake category and the actual vortex produced by the 757. In my experience as a BA 737-200 Capt I had one too many encounters at one minute spacing so always then insisted on two mins. The effect of catching a 757 wake is to be rolled at about 90 degrees a second and that needs FULL opposite aileron and a touch of rudder. Try it at about 400 feet for a real adrenaline rush! If your clients want 2 mins behind a 757 I'd let them for safety's sake alone.....