There are many - in almost every task the i7 will outperform that FX.
The FX 9590 is an overclocked FX 8350, so you're paying a huge premium for an overclocked version of a cheaper CPU. Intel has far better per core performance (due to its higher IPC) than the FX series. In addition, the FX has a much higher TDP (220W I believe, compared to maybe something around the 100W mark for the i7?).
Both technically have '8 cores' - The FX has 8 cores but each shares a module, and the intels have 4 cores that each produce virtual cores which are not quite as strong as physical cores.
The intel will be faster in most tasks at a lower clock speed. In addition you will need a higher end motherboard for that FX since there aren't many that support it's huge power requirement, whereas you can be somewhat comfortable putting an i7 4770k in a cheaper motherboard (unless you're planning to overclock).