Generally, low end CPU will bottleneck good GPU. i5 2400 is not that bad at all. You can opt for GTX 760 in your case.
Uh.... your cpu is a lot better than your video card. A GTX 760 would turn your system into a very good gaming PC.
Oh that's good to hear, usually I hear of people having i7 3770k or i5 3570k in their builds so I mostly just assumed that a i5 2400 wouldn't handle those cards as good