You need more vcore to get higher. You need to be around 1.375 to 1.45 for 4.0Ghz if your chip will run the number. Every Ryzen chip I have tested does between 3990Mhz and 4091Mhz. That is a sample size of 7 processors. Turn up the pump speed to max on the Kraken and boost your fan speed to manage thermals and push a little harder. The 8700K is better in some scenarios and the 1700 is better in some.
I have to agree with ccoke. I did the same Change (1700 to 8700) and it wasn't that much of a difference for me. Maybe I was lucky with the lottery?