I had the same question except I have a core i7 3930k (currently at liquid cooled stock 3.2 ghz that I will be overclocking to about 4.0ghz)
I just bought the computer and I have a single 6870 so getting a high-end video card set up is kind of set off for future and gradual improvement... any advice?
You are definitely going to be GPU bottlenecked under virtually all circumstances, overclocked or not. Depending on your resolution and what games you play, you still will get good gaming performance in most cases, it's just that your CPU isn't going to have to work hard. If you have a 1080p or lower monitor your 6870 will do well in most titles, with only the absolutely most demanding games causing it to struggle. At this point, I would say wait for the HD 7000 series to hit and see how they perform. You then have the choice of buying a newer more powerful card, or maybe snatch up another 6870 when prices drop on them due to retailers wanting to clear out old stock, depends on how much money you want to spend on a GPU upgrade.