Hi Gerrit03,
Your mainboard MSI 760GA-P43(FX) should be able to handle the R9 280 along with your Athlon II X4 640. I suggest to up a bit the RAM to 8GB and make sure you have a good power supply to power the system and the GPU. Here is a good page that explains the CPU / GPU bottlenecks in case you find any,  you can still make adjustments to make sure that you are setting your system they way you want it. Here is the link