i-7 is fine for the 3080, 3090 is more powerful so if you will need the i-9, no point of not having the best cpu when you have the best GPU, plus you will only see improvements in 4k and 8k with the 3090, you can do 4k 120z with both cards, but you will have to turn off more effects to get those frames up
if you just starting out, its better you just get a pre build pc for 2000, that has all the best components, so you just need to switch out the GPU when you want to upgrade, My PC was built in 2017 and all I need to upgrade is the GPU because all the components were top notch, my power supply was 750w over kill for the 1080ti I had, you have to look at has a long term investment, plus you can always part out the PC when you want to build one from scratch or buy a new one
nowadays you can finance all these PCs and parts, all you need is a bank account not even credit, works the same way as ABC warehouse type approvals, or you can just get financed by best buy you only need a 630 credit score and you can be paying 30 dollars a month for the new NVIDIA card
also you can't go off benchmarks
because every game is different
some games are more CPU reliant, so if you have the same CPU the FPS will be around the same, because the game itself draws more on the CPU for the frame rate, and at 1080p the CPU is always the more dominant factor which is why you barely see improvements at 1080p between the 3080 and 20 series when you see the test
somebody got a video on youtube of them playing Doom in 8k with all the shyt on in 60fps with a few drops here and there, no graph shyt
like I said when you get into PC every game is different, that's why they have the settings menu so you can optimized the game to your liking
sometimes you can turn off stuff and it doesn't change anything in the game it was just wasting resources and get a frame rate boost
other times the effects make a huge difference and don't want them off, and will take the frame hit, etc
its all preference which is why you have settings to begin with
