Which would be better for FSX, Intel 3570K running at 4.4 Ghz  or an Intel 4790K running at stock 4.0 Ghz? These would be married with an Nvidia 660 card.

4790k because it turbo boosts one core up to 4.4ghz. If you turn turbo boost off, I would suspect a 3570k overclocked that much would edge out the 4790k by less than 5%. All of this is just speculation though, nothing to back that up. 

I would also say 4790 - you should be able to run the 4790K at 4.4..