I53570k vs fx 8320

I have one of each. For my usage, it is hard to tell a difference in actual use. I do think the i5 is generally a little faster. If you run many applications though, or your applications are all well-threaded, you might not notice a difference.
Over time, the i5 will also use less power. It also runs cooler. Keep in mind you can get a cheap mobo and still get good performance from an i5, but a cheap mobo with the FX-8320 may be old tech that will hold it back, or it may have undersized VRMs that ultimately won't be able to handle the load (especially if you OC). See this spreadsheet: https://spreadsheets.google.com/spreadsheet/pub?key=0AgN1D79Joo7tdE9xMUFlMEVWeFhuckJEVF9aMmtpUFE&gid=0 for examples of what to avoid due to VRM problems.
 
^That is true, as they favor single-thread performance, at which the i5 is notably better. With the same graphics card in either build, I'd choose the i5 myself. The FX is certainly not bad, but in a number of small but measurable ways the i5 will be better. And, as I implied earlier, although the FX-8320 is cheaper, a proper motherboard (and cooler, especially if you OC) will likely make up the difference in cost compared to an i5 with a cheaper board.