What do you mostly do with your computer? If gaming mostly what monitor and at resolution?
If it is gaming, and it were me, that GTX970 is getting a bit long in the tooth, I would consider a new GPU first.
I have the 8086k and it is a great CPU, but at some things my 5930k if faster on some BOINC projects and my 3930k holds its own.
Maybe a 1070Ti, 1080, 1080Ti, 2070, 2080. Would you consider used? I have seen used 1080Ti and Titan Xp selling for 500-600$
If you do rendering or data processing, you may want to look at something with more cores and maybe better/newer CPU instruction like AVX2 and whatnot. 
Something in x99 may fit the bill with more cores or AMD threadripper.
Is that 3930k over clocked? Consider bumping it up to 4.2 or better for more speed if it is not?
Budget?
A little bit more info would help people give you a good recommendation on what way to go.