The GTX 650 will be compatible with your system. Though you might want to check out the CX 430, it's often on sale and would give you a bit more overhead.
You would want a dedicated GPU for high detail settings at 1080p, but the integrated GPU will handle both those games well at 720p medium-low settings.
I suggest getting yourself a GPU, playing games like Skyrim without a GPU will put a high load on your CPU and RAM, which will shorten the lifetime of those components.
The GTX 650 will be compatible with your system. Though you might want to check out the CX 430, it's often on sale and would give you a bit more overhead.