The real life performance of a processor cannot be judged by any benchmark tests,as in real life several factors influence it like how much game is optimized for a processor (Like consoles), even the ambient temperature play a crucial role.On G2020 I can easily play Gta5 paired with r7 240 over clocked to 950mhz on a minimum medium setting with smooth fps(35-40).
Rx550 being new will receive new games that are optimized for it.
So I don't think so that RX 550 is slower that gtx660ti.