Berwyn Jones of Wakefield Trinity in the mid 60s was pretty nifty. Not surprising as he had represented GB in the 1962 European Athletics Championships and was regarded as a certainty for the 1964 Olympics had he not turned pro.
Wilf Rosenberg, a South African winger was also pretty nifty for Leeds around 1960 - 63 but lost all his confidence when his face was rearranged in a tackel. He scored 48 tries in 1960/61.
I imagine that Olympic bronze medallist McDonald Bailey was also pretty speedy but he only played 1 game (for Leigh)