If you are OC'ing, all you need to add is good chip (Venice 3500+ ?), good ram (lots out there), and a good HSF. The 6800GT has tons of potential, your MoBo and PSU will work well with OC'ing as well. I will tell you this: OC'ing can be quite frustrating sometimes. You may seem to have a nice stable overclock, only to find that one of your favorite games' innate instablity is magnified by the overclock. . .the occasional CTD, even if one every 20 hours, can be quite annoying if it comes at the wrong time! Additionally, there is no question that a 3500/3700+, 6800GT, and 1 gig of ValueRam will provide excellent performance right now.
It all comes down to what you want. The price difference between adding a Venice core and high-quality OC'ing ram and HSF is what, $200? $250? You will have to decide if it's worth the investment, and no one here can answer that question for you.
Come quite a way from your initial post, eh?