Which CPU should I get?

[sasmp5ninjaz]

I am currently building a gaming PC and want it to be a top end build. So far I have;

RAM: Hyper X 16gb ddr4 2666Mhz
SSD: 500gb Samsung evo
HDD: 2tb WD black
CPU cooler: be quiet dark rock 4
Case fans: 2-140mm be quiet, 1-120mm be quiet
Case: NZXT H500
MOBO: MSSI Z370M gamign pro ac
https://www.msi.com/Motherboard/Z370M-GAMING-PRO-AC.html

I am stuck on what to buy for my CPU and GPU. I was going to buy a I7 8700k and a gtx 1080ti however due to cease of production a gtx 1080ti's price has risen to upto £900 now. I was looking at getting an RTX 2080ti as they're just over £1000 and I have the budget to. I want to game at 1440p 144hz.

on the MSI website for the motherboard, linked below, a recent BIOS update states it it supports 9th gen intel cpus and in the specification i9 cpus. Am I correct on this? I am looking for more confident advice from people who know whats best before I make any purchases and want it to be the best I can get it to be.
https://www.msi.com/Motherboard/Z370M-GAMING-PRO-AC/Specification.

I have 2 problems:
Do I stick with the i7 8700k and get the RTX.
or do I go for the I9 9900k and RTX GPU.

Thanks for any help you can give, I appreciate it

 

[Obakasama]

Unless you can update the BIOS without a CPU (some motherboards allow it but not all), then the i9-9900k (while a better performer) is a risky starting point as it may not be usable out of the box. You'd still need the updated BIOS for it to work.

 

[atomicWAR]

Yeah Your better off with a Z390 board as you know the bios is setup for the new 9th gen chips.

 

[sasmp5ninjaz]

I do have an I5 I can use but I think I will stick with my gut an go for the I7. I have already got the board so I understand where atomic is coming from. The I7 would be more then enough power and I can always OC if needed.
Thanks for the help guys