Thank you all for your comments and suggestions. Now let me clarify some things.
I cannot overclock my i7 8700k higher than 4.7ghz, even 4.8ghz is not stable, I tried and tested it many times and cannot go higher than 4.7ghz. On top of that, the 8700k at 4.7ghz is already bottlenecking the overclocked 2080 Ti. I cannot delid the CPU because already have a different owner and that person is fine with 4.7Ghz (he does not care about OC), btw my old system is already sold (but not my PSU).
Apart from gaming, I process, edit and export 4K videos every day, a better CPU than the 8700k would really help me too. I do more daily work on my PC than what I listed here but is not relevant to the hardware because is Database programming work. It may be, in the near future, that I will need to process some 3D work with After Effects and/or Autodesk 3ds Max.
For gaming, I do play in 4K, but I also record playthroughs, benchmarks, performace reviews, etc. for a youtube channel. So having the RTX 3090 will ensure max performance on the GPU side. The 3080 20Gb that may be released in December looks like a good option but is listed as the same amount of CUDA cores as the 3080 10Gb, I bet it will not beat the 3090.
EDIT: The RTX 3090 will arrive in 10 days, so still, need a good combination of:
CPU
Motherboard
RAM (non RGB)
Motherboard must be solid for overclocking CPU.