Performance problems

[Naughty-Boiii]

Hello, I have just bought a new graphic card (Sapphire RX580 Pulse) and i have problems with the performance because m,y friend has RX 570 and has always 20-30-40 FPS more than me with the same settings, i have tried overclocking, underclocking, undervolting, Fresh windows, nothing seems to affect 

My specs are 

i5 7400

RX 580

8gb DDR4 2400 Single channel

and also the graphic card requires an 8 pin power cable but my power supply doesnt have it so i use 6 pin instead as i read some topics say its fine.

Thanks for any help possible

[Epimetheus]

Well, what cpu and ram configuration does your friend have? 

[Naughty-Boiii]

30 minutes ago, Epimetheus said:

Well, what cpu and ram configuration does your friend have? 

Same ram CPU i5 8600