With just 8gbs of ram, you will use about 2-4gbs on windows alone. Once the remainder ram fills up, your pagefile/swap file/virtual file will be used as memory. This is very slow. This is why you have stuttering.
@thestryker has a good point. An SSD for your boot drive (and gaming drive) would help speed up your system. Games on it load faster, and although it doesn't affect FPS really, at least your swap file will be faster than on a HDD,
What temps are the CPU and GPU at when gaming?
Your CPU may also be maxing out, which is another thing that can cause problems.