Seeing as I assembled it last summer for around £300, I'd say its fairly average for a modern computer.
Now you mentionn stuttering, I get a bit when an AI car comes into view for the first time - presumably loading the model, but I don't get any high speed stuttering at all, not enough free ram to cache enough of the island perhaps causes it?
Btw, I run 1280x1024, high detail, no AA/AF, HDR off, and average 35-40fps. Upto 50fps when out in the sticks. Mild overclocking on the CPU & gfx card.