Yeah, would have to agree, the graphics card is probably the weak point among that. 4670 is at the bottom of the scale(in the 4000 series) with regard to desktop graphics. (x8xx > x6xx for example, then in the minor scale of things, xx70> xx50, with a 4870 being largely better than a 4670, a 3870 would probably still sit above a 4670.
6850 would typically be around £115 if you were looking to upgrade, though that still below the insane 'recommended' spec of a 6950.
Also, Conversely, if you were looking to upgrade, ATI are due to release a new bout of graphics (7000 series) in 'Q4' whenever that is.