Yeah, I don't think anybody sane is saying that the 4770 isn't hands-down better than the FX chips, but you have to weigh the pros/cons and pricing
If the OP doesn't want to change mobos, then the 8320 or 8350 + a good air cooler + low to mid 4Ghz OC is probably the best buy.
If he's willing to sell the mobo, then going 4770K + Z87 Asrock is a much better buy than going 9370 or 9590, as that pricing range starts to make little sense from the AMD side.
Being that OP is running a 780, personally I'd lean towards just selling the mobo and going 4770K, but OTOH, it's more hassle, and it's not like the 8320/8350 are terrible performers at 4+Ghz. In some poorly coded games the 4770 will have a HUGE lead, SC2/Skyrim (and presumably the upcoming FO4 if it uses the Skyrim engine, which they probably will considering how well Skyrim sold, why change engines when people are willing to plunk down the bucks). On most games though, a 4Ghz+ 8-core FX is more than fine. I defy any single GPU user to tell the difference in a blind test with probably 80% of titles. BF4 for example, it's not going to feel any different unless you are running some monster GPUs with a great OC. Single 780 at 1080P Ultra or higher? It will work great either way.
The better USB/SATA/PCIe performance and lower power would make it a no brainer to me personally, but I can't say the 8320/8350 are a bad bet either for ease/value. I *can* pretty fairly say that the 9370/9590 are a bad deal.