A stock 9900k with cheap 3000 MT/s RAM is not going to be a performance king of anything. You need to add faster RAM and a decent overclock.
If you run your 9900k at stock with 3000MT/s RAM, your performance will not beat a 3800x overclocked correctly. Here is a 9900k stock no MCE and 3200MT/s RAM with a 2080ti in Shadow of the Tomb Raider.
source
https://www.guru3d.com/articles_pages/palit_geforce_rtx_2080_super_gamingpro_review,13.html gives 134fps average for a 9900k stock and 3200 RAM @1080p.
Shadow of the Tomb Raider 4k highest 9900k @ 5GHz G.Skill Trident Z RGB DDR4-3600 2 x 16GB (17-18-18-38)
https://www.anandtech.com/show/14663/the-nvidia-geforce-rtx-2080-super-review/4
Vs. a 3800x 3800MT/s CL15 RAM with a RTX 2080. 1080p
Vs. a 3800x 3800MT/s CL15 RAM with a RTX 2080. 4k
As you can see the 9900k with 3200MT/s RAM (an overclock) a 2080ti loses to a 3800x with a 2080 and 3800MT/s (overclock) RAM. RAM speed matters. Note that the 3800x is bottlenecked by the RTX 2080, when the 3800 RAM was CL16 it hit 141fps average.
Now with the 9900k system @ 5GHz 3600 32GB CL17 RAM with a 2080 ti matches the 3800x 3800MT/s CL15 RAM with a RTX 2080 @ 4k.
Spending a bit of money on better RAM will help performance, not all 9900k's overclock well and RAM will help keep the performance good. Also there is the issue of getting a 9900k at 5GHz cooled correctly.
A stock 9900KS with 4x8 GB DDR4 3200 CL16 MHz (Corsair Dominator) 11586,
Intel has released its flagship desktop processor in the non-HEDT segment. The 9900KS is their most premium Coffee Lake-S eight-core processor that has been discussed so abundantly. This little beast ...
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My 3800x IF 1900 RAM 3800MT/s CL15. 11571 maximum, 11500 average good run. (score varies a lot for no reason in 3d mark with the 3800x. In cinebench r20 you could hit 5200+ each time you run but get 10900 in time spy cpu the first time, then 11500 the next time, etc turning off cpu-z and gpu-z appears to sometimes help fix this via FMSIDiag.exe )
https://www.3dmark.com/spy/11749223
12337 Time Spy
https://www.3dmark.com/spy/9310157
Note: My 3800x has a full customer water loop, 360x60 copper rad with 6 push/pull fans. IF is 1900 and RAM is 3800 MT/s with tightened timings.
Having a fast 9900k system is not just a matter of spending $3000.