First post here but have been enjoying your site for a while now! Found these specs on the web for the 757-200:
Operating empty with P&W engines 57,840kg (127,520lb), with RB211s 57,975kg (127,810lb). Basic max takeoff 99,790kg (220,000lb), medium range MTOW 108,860kg (240,000lb), extended range MTOW 115,665kg (255,000lb) or 115,895kg (255,550lb).
So it seems that although all 757s are treated as heavies due to their inherent wake turbulence, the only one that can be officially classified as such is one of the two extended range versions (w RB211s?). Anyone know who flies this particular version?