Flagship Z390 vs Budget Z370 Motherboard
We have two final graphs we'd like to discuss which compare the performance of Intel new 9900K on a flagship Z390 motherboard to that of a budget Z370 motherboard, MSI's Z370 PC Pro packing a real 4-phase VRM and for reference I've included the Core i7-8700K and Threadripper 2950X results.
Starting with the stock out of the box performance we saw that the MSI Z390 Godlike allowed the 9900K to produce a score of 2048 pts. Now slotting that CPU onto the Z370 PC Pro resulted in a score of just 1790 pts after a 6-run average. Initially the score was up around 1900 pts but on the second pass we saw a lot more VRM throttling and this continued as we ran the test 4 more times to report a 6 run average.
This meant on average the 9900K was 13% slower on the budget Z370 board. It is possible to enter the BIOS and remove the power limits and this did see full performance restored but even then we still saw some VRM thermal throttling going on and I did have a 120mm fan directly over the vcore VRM heatsink. So this is likely shortening the life of the motherboard and I don't recommend removing the limits on boards with them in place.
Interestingly, if you overclock the 9900K on the Z370 board with the limits in place the performance is much worse than if you did nothing at all. Basically the increased vcore voltage sees the VRM throttle even harder with the limits in place and this further reduces CPU core clocks. Again removing the power limits does mostly restore performance to what was seen on the Z390 board, but if you were placing this board under heavy load for extended periods on a regular basis I don't imagine it will have a long and happy life, likely expect fireworks in the short term.