What are you saying, you'd want to replace your whole system with OcUK's 2.6K system? Money growing on trees?
70 frames per second isn't low, are you sure your graphics cards are actually playing up? You certain it's not the at the games end and not your system? Try testing with other components as opposed to purchasing a completely new package PC, at this rate you'd never really know what was the actual problem. Try the SteamPowered forums for some expert advice, I'm on a 7800GT myself and have experienced some FPS jumps. Also, I wouldn't base 3DMark scores going down as a hint that one of your components have gone "bad".
Again, just noticed the topic title, don't go for it if you're system is actually fine.