You have to look at your net gain for cost(return on investment)
What will gain you the most for the money you have to spend.
I was in a similar predicament not long ago as I have been on an old 1155 platform i5 3570 for years and my GTX 760 cards were not doing as well as they were 5 years ago.
My options were a GPU upgrade and I had one CPU upgrade option left on that platform.
A 5700 xt that ran me $380. A i7 3770k was $99
My other option was $450 for a 10600k and socket 1200 MB since anything less would be throwing money away, and would still be hobbled with a GPU that wasn't going to go faster no matter what CPU was pushing it. New DDR4, and probably a power supply.
It was an easy choice as the 3770k runs just fine on the couple AAA titles I play and feeds the 5700 xt well, everything is happier in my system compared to the i5.
There might be a z590 socket 1200 in my distant future, but way down the road. I obviously am not a bleeding edge hardware guy though, and can't justify spending the money on it.