I have an 8 year old machine with a pentium 4 2.53 ghz cpu, and i went for an ati hd2600 pro as i saw one cheap on ebay with no bids, i got it for £31 about 18 months ago, and with lynces hi res textures, running aa/af at 4x and a 1024x768 32 bit res i can achieve about 80 fps on my own on most tracks and ~45 fps online, which isnt the best in the world, but fit for purpose on this old rig, but i do get the odd t1 fps dive where it all goes a bit slide show like gameplay, but thats the cpu causing that as it maxes out at 100% in that situation.