I5 4670k/4690k with r9 280x

The FX-8350 is up to 45% roughly slower than a top-end i5 Intel CPU such as for Skyrim which doesn't use many cores so works far better on the Intel which is better per core.

i5-4690K?
Awesome CPU, however you could buy an i5-4440 for cheaper and put the difference in cost to a better graphics card which would be better on average as most current games benefit more from a better graphics card and an i5-4440 is usually plenty on the CPU side.

It depends a lot on how long you intend to keep the PC as well. The i5-4690K with a good motherboard should last at least five years on the CPU side of gaming. You could then simply replace the 280X card with a better one in a couple years and not worry about any potential bottlenecks.

It also matters if you do video editing or other tasks.