Depends on the game. There are some games where the FX 9590 would have an advantage. If you compare the FX-8320 to the i5-3570K (very similar clock speeds) the 8320 is faster in heavily threaded applications (sometimes; naturally it depends on the specific application). The FX-9590 is the same as an 8320, just at 4.7-5GHz. So by that logic it would still be better in those same situations than an i5 3570k at 4.5GHz.
That said, in most games the 3570K is better as very few perform better on the FX eight-cores than on Intel i5/i7s... reason being that even though they use many threads, they still tend to load up the major components of the game's engine onto 1 or 2 cores, so single threaded performance still helps a lot.
So really it depends on the game. If you were to play something like World of Warcraft, your performance would be significantly higher than his. But if you played BF4, he might pull ahead by a few frames per second (though honestly in heavily threaded games it's hard to notice a difference since at that point the GPU matters more).
And it might slightly bottleneck crossfire 290X, but it should be fine. I know people playing with crossfire 280X on an FX-8350 @ 4.5-4.9GHz while being <75% CPU usage, so 290Xs should still run really well but they may not perform quite as well as they would with something like a 4930K.