The 757 wake vortex was indeed powerful. Sitting in the garden of the 'Railway' pub at Mobberley when MAN were landing easterlies it was the only aircraft (inc 747s) that produced that weired whistling rushing sound of wake vortex.
I noticed on 505EA and subsequent examples I flew in belonging to Britannia, Monarch and Air 2000 that there was a noticeable sideways oscillation at the front end on climbout whilst accelerating through about 250 kts. It only lasted about 15 seconds but was quite noticeable.
Mate of mine used to fly them for BA. He says a firm touchdown would produce what they used to call a 'wet dog' landing; the whole aeroplane would shake laterally from tail to nose, like a dog shaking itself on getting out of a river.