Depends on the application. If the application is heavily multithreaded it's likely the 970 will be slightly faster. If the application isn't as multithreaded the 2600K will be faster.

In FSX?

I don't know.

Remember that the 2600K uses a much newer and better design than the 970. So each core on the 2600K is faster than each on the 970 even at the same clock-speed. I would get the 2600K because while it has less cores, each core is significantly faster. In most games the 2600K will outperform the 970. It's also cheaper, easier to overclock, puts out less heat, on a platform that won't be discontinued at the end of the year (X58 will be).