@mrc545 Your CPU load seems pretty high in both reports.
This strikes me as too high. My i7-8700K (6 cores) only runs at 20% with a 1000 MP/s load (BI in service mode with console closed) and this is without any Nvidia hardware acceleration, and several cameras not even fully tuned for CPU efficiency (not all of them use direct to disk and hardware acceleration!). When I open the GUI full-screened on a 4K monitor (fed by Nvidia card) CPU usage only goes up to 45%.
By all rights your i9-9900K should have been processing only about 20% more video than my CPU, and the 33% increase in core count should more than make up for it.
While that is an improvement, it is still far from what I would expect to see. Why aren't you using Intel decoding on all the cams anyway? Nvidia's decoding is horribly inefficient in terms of energy used.
One thought, maybe Windows is underclocking your CPU for some reason and playing with the Power Options would reveal the true load. My 8th gen CPU for example regularly bounces between 4.3 and 4.4 GHz but maybe yours is running far below that.