They will be basically the same as far as CPU upgrades. Price would be the most important but I would recommend the 760K is these are the CPUs you are looking at.
The 760K is Richland based while 5600K is Trinity. The 760K will overclock better and higher (if you plan to OC) and the stock clocks should be higher than the A8 5600K. At the end I would choose what is the cheapest as both will OC to a decent 4.5GHz at the least. The 5600K will probably run hotter due to the IGP, not sure if it will use less if the IGP is disabled.