well here you go. I lowered my 192sp gtx260 to 460/1600 which is 20% slower than stock. that would put it pretty close to a 4850. I used very high settings and even 2x AA so it would be pretty gpu intensive. I ran these at 2.0 and stock 3.16 on my E8500. his cpu at 2.4 E4600 would not even be as fast as an E8500 at 2.0 but Ill give you/him the benefit of the doubt.
Settings: Demo(Ranch Small), 1280x1024 (60Hz), D3D10, Fixed Time Step(No), Disable Artificial Intelligence(No), Full Screen, Anti-Aliasing(2x), VSync(No), Overall Quality(Very High), Vegetation(Very High), Shading(Very High), Terrain(Very High), Geometry(Very High), Post FX(High), Texture(Very High), Shadow(Very High), Ambient(High), Hdr(Yes), Bloom(Yes), Fire(Very High), Physics(Very High), RealTrees(Very High)
1280x1024
cpu at 3.16 GTX260 at 460/1600
Total Frames: 2675, Total Time: 51.01s
Average Framerate: 52.44
Max. Framerate: 83.45 (Frame:411, 6.59s)
Min. Framerate: 36.61 (Frame:1841, 35.60s)
cpu at 2.00 GTX260 at 460/1600
Total Frames: 2120, Total Time: 51.01s
Average Framerate: 41.56
Max. Framerate: 67.26 (Frame:348, 6.76s)
Min. Framerate: 27.73 (Frame:802, 17.04s)
Settings: Demo(Ranch Small), 1680x1050 (60Hz), D3D10, Fixed Time Step(No), Disable Artificial Intelligence(No), Full Screen, Anti-Aliasing(2x), VSync(No), Overall Quality(Very High), Vegetation(Very High), Shading(Very High), Terrain(Very High), Geometry(Very High), Post FX(High), Texture(Very High), Shadow(Very High), Ambient(High), Hdr(Yes), Bloom(Yes), Fire(Very High), Physics(Very High), RealTrees(Very High)
1680x1050
cpu at 3.16 GTX260 at 460/1600
Total Frames: 2466, Total Time: 51.01s
Average Framerate: 48.34
Max. Framerate: 70.07 (Frame:368, 6.34s)
Min. Framerate: 34.56 (Frame:1656, 34.44s)
cpu at 2.00 GTX260 at 460/1600
Total Frames: 2040, Total Time: 51.01s
Average Framerate: 39.99
Max. Framerate: 67.26 (Frame:329, 6.37s)
Min. Framerate: 24.37 (Frame:661, 14.41s)
at 1280 the faster cpu provided 27% better average and 33% better minimum framerate. at 1680 the faster cpu provided 22% better average and 41% better minimum framerate. in any case at both resolutions the slower cpu would be noticeably slower especially at minimum framerates. if he isnt going to oc that cpu then he wont even get all that a 4850 can do especially in a game like Far Cry 2 that will use that extra cpu power.
a small oc to 2.8 to 3.0 will easily eliminate 99% of any cpu limitations at 1680 with a 4850. a 4890 would need a little more boost than that to be fully effective. of course most games will be perfectly playable with his cpu at stock and a 4850 but a little oc on that cpu would really help in many of the current games.