I guess cf 7870 or sli 660. After that I would expect at least some bottlenecking. I have seen a single gtx 680 get bottlenecked by 8350 in skyrim. If you going to get better cards, get at least i5 4670k or processor or equivalent preformance.
there is no bottlenecking it comes down to the core use in games ones that are set up for multi threading will have no problem at all. Games that are poorly optimized and use one core like skyrim will not be as good as a intel cpu because amd core is weaker. but will be easily in the playable range no matter what.