What a Core i9-9900 is good for
This chip is capable at 1080p with a mid-range card, but it will become the limit if you pair it with something substantially faster. If you are considering a large graphics upgrade, check the pairing first — you may find most of the new card sitting idle.
Moving to a higher resolution is the cheapest way to get more out of it, because it shifts work onto the card and away from the chip.
A small cache holds this chip back
16 MB of L3 is modest by current standards, and it costs this chip more in games than its clock speed suggests. Game engines walk large, scattered data structures, so a small cache means more trips to main memory and more stalls on the render thread. Memory speed and timings matter unusually much on a part like this.
A note on age
Released in 2017, this chip is 9 years old. Beyond raw speed it is on an older platform, which usually means slower memory, fewer PCIe lanes and no path to a newer processor without replacing the motherboard. Factor that into any upgrade maths — the chip may not be the only thing you end up replacing.
Where it sits
Ranked 134 of 201 desktop processors for gaming. Nearest faster: Ryzen 5 5600F, Ryzen 7 3700X. Just below: Core i9-9900K, Core i9-9900KF. Full method on the methodology page.