RO is very CPU intense due to ballistics and network calculations (all the zones, anti-portal etc. stuff that determines who can see and who can hit whom)
I run an AMD X2 5000+ (at 2.6GHz) and I do not get constant 60FPS (vsynch) on maps with large outdoor firefights. If I run without bots, the graphics alone will not slow me down, it's the shooting and fighting that taxes the CPU down. Even modern processors can suffer from certain maps.