Not sure if its really an AMD problem..Im using a AMD Phenom ii X2 965, 8 gigs of ram, GT 710 GPU, I dont have lag at all with any version of RoR.
If your game is staying at 60 Fps, Turn off Vsync in the Nvidia control panel, as well as in the ROR config. I had a problem with it staying at 60 fps, turned it off, and now im in the 200's at all times.
This can actually help with a lot of games.
CS:GO
Vsync: 30 Fps.
No Vsync: 174 Fps.
RoR
Vsync: 60 Fps.
No Vsync: 200+ Fps.
Gta IV
Vsync: 16 Fps
No Vsync: 42 Fps
Remember, This is my setup, yours may be different, and it could honestly come down to anything. I would recommend looking around on Toms Hardware, You can fix anything if you read through enough forums.