http://cpuboss.com/cpus/Intel-Xeon-X5660-vs-AMD-FX-9590
2.8ghz 32nm 6 core. (9590 is the 8350's OC speed but the xeon is locked)
http://cpuboss.com/cpus/Intel-Xeon-X5560-vs-AMD-FX-9590
2.8ghz 45nm quad core.
It looks like adding 2 more cores, helps. So having 8 cores with the pair of Xeons would be ok.
I am going to say the fx-8350@4.7ghz and pair of X5560's would be a close tie.
Both systems also have the same issue too with slow single core speed and games and apps not using all the cores and threads.
Putting two used 6 core Xeon cpus would give you 12 cores with 24 threads. (Check to see if the board works with 32nm 6 cores first)
Both can be overclocked by about 1ghz.
http://cpuboss.com/cpus/Intel-Core-i5-2500K-vs-AMD-FX-8320
(always the big question...Won't intel's locked i5 make it lose to amd's when overclocked?) For the most part yes, but when you consider the i5 is only 68.25watts vs 178.75W, it will depend on the intended use.
Intel's budget locked i5-4460 vs. FX-8350@4.7ghz (fx-9590)
http://cpuboss.com/cpus/Intel-Core-i5-4460-vs-AMD-FX-9590