Take a very powerful card like the HD 6990, this has been blasting through games ever since the release, and may continue to be a very viable option until DirectX is updated. But let's talk about your system. The CPU is good, you have enough RAM, GPU is pretty high end and your motherboard too. Should last about 3 years on high settings but I cannot be sure. Instead of worrying too much about the future, enjoy it now!
Lol, "GPU is pretty high end", it's the best single GPU you can get from Nvidia, the only way you could go "more" high end is by getting a dual GPU solution.
So yes, it will last you about 3-4 years at least, I reckon. I had a 8800 GTX for 4 years and was still able to play most games at full details at the end of those 4 years (even though it was only DX10)