If possible get the SAME RAM that you already have and update your BIOS (if needed) as BIOS updates often contain RAM profiles.
You'll want to choose "XMP" for the default RAM profile unless you are overclocking the CPU (in which case you'll want a better cooler, assuming that CPU supports overclocking).
I think you'll see some severe bottlenecking at times in some games, but the important question is whether it's worth buying a better CPU for the improvement. There's quite a huge variation between games. I tried to find a comparison of an i5-3570K to your CPU but couldn't (or even the i5-3570K to an i3-3220 which is also dual-core).
If you were buying a GTX670 or higher I might recommend selling your CPU and getting an i5-3570K but I think I'd have to recommend keeping your CPU. As I said, unfortunately a good comparison between the i3-540 and i5-3570K is difficult to find (for me).