I run a 980x on a Asus R3E board at 4.2Ghz and see about a 10FPS drop compared to my 4670k at stock speeds, both using a 980 SC.
The G3258 vs 980x in single core the G3258 will win but anything after that the 980x will beat it. If your multitasking or gaming/streaming the 980x is the way to go. Now if you want to turn around and sell the 980x system and upgrade yours that would be a better option. But if your just comparing the two I would move back to the 980x build, plus the 1366 sockets are just fun to overclock.