I haven't seen much discussion in these forums about overclocking the CPU, so think it would be helpful to add to this topic my experience with overclocking.
First of all, if you are running your playfield at 4K, it appears to me that you need as fast a CPU as you can get. I base this belief on the observation that my tables usually run at about 180 FPS, but regularly dip down to just over 60 FPS for short periods of time. This tells me that my video card is more than capable of delivering the performance needed for a good Visual Pinball experience, but that there is a bottleneck somewhere in the software (the COM interprocess communication perhaps). If the bottleneck can't be eliminated, then the best we can do is tweak settings and increase CPU speed to reduce the bottleneck.
So I proceeded to overclock my i5-7600K from its stock 3.8-4.2 GHz speed up to 5 GHz. I was able to do so while maintaining a CPU temperature around 73 degr C. However, using the HwInfo app, I saw CPU speed throttling events happen, and something called AuxTin1 hitting temperatures around 175 degr C.
After doing some research, I found that AuxTin1 could represent the voltage regulators. The voltage regulators depend on air being blown onto the motherboard for cooling, as happens with stock CPU coolers. The CPU cooler that I am using (Cooler Master Hyper 212 EVO), and probably most non-stock coolers, does not blow any air down onto the motherboard.
The motherboard that I am using has a heatsink near the CPU and voltage regulators, which I assume is meant mostly to cool the voltage regulators. So my solution was to position a small fan over the heatsink. Doing so caused the max AuxTin1 temperature to drop to about 107 degr C, and the CPU speed throttling events to cease, allowing me to enjoy an excellent 4K Visual Pinball experience.
I hope some other members find this post to be helpful. 
ASRock Z270M Extreme4, i5-7600K, 16GB G.SKILL TridentZ DDR4 3200, EVGA GeForce GTX 1070 SC
Samsung 850 EVO M.2, Samsung UN40JU7100 4K playfield, Samsung SynchMaster 2232 backglass, Pinscape on VirtuaPin Plunger Kit v3