Have you been monitoring temps on your processor? I would recommend you download Real Temp and see how well the processor is being cooled. Or download Hardware Monitor and check overall system temperatures. Your graphics card will probably display temps in whatever software the manufacturer provides.
To answer your other question: Your system is fast enough not to bottleneck your card.
Check the temps and see how they look, but my hunch is that you'll want a better case than that to house your components. Especially if you're planning on adding another 460.