The i5 4670k has a 3DMark11 Physics score of 6820, whereas the FX-8350 has a physics score of 6870 so it's a tad faster in that respect.
That doesn't paint a whole picture though, and you should know that the i5 has fewer cores, but they are stronger, whereas the FX-8350 has more cores, but they are weaker. That means the i5 has better single-threaded performance and the FX-8350 has better multi-threaded performance.
In Crysis 3, Far Cry 3, and Battlefield 4 (which take advantage of as many cores you can throw at them) the FX-8350 comes out on top most of the time. However, in older games and applications that don't utilize multi-threading the i5 4670k wins out most of the time.
So there you go, both are fantastic processors and each has it's strong suits.
TL;DR go with the FX-8350 if you use a lot of multi-threaded applications, go with the i5 4670k if you use a lot of single-threaded applications.