AMD6415, you CPU is fine. It will run the games out now without a problem. It will not bottleneck a 3870, so don't worry about that.
Yes, there are faster CPUs on the market, but you are in good enough shape to run whatever you want. To upgrade would require a new mobo, CPU, and RAM... which won't be cheap. There is NOTHING wrong with using what you have now. you may decide to upgrade in the future, but you are in good shape now.