@david988 they are the same CPU only difference is 4.4 turbo(all core) on the 9600k vs the 4.1 turbo on the 8600k but that 300Mhz doesnt do much in games they perform the same at stock speeds. The different is less than 1% which is usually "margin of error" anyway.
@david988 yes cause 8th gen isn't being made anymore only 9th gen (even though 8600k=9600k) @tforulez same thing for the 6600k it's just been discountined for awhile so they have a few and stock and have kept prices high in my country nothing other than 9th gen is avalaible for purchase (and ryzen)
Also Intel had those shortage issues with 14nm for awhile 10-6 months ago so the prices were higher when i bought my 8600k it was 300€ (december last year) but now its out of stock and the 9600kf is 230€ so theyve dropped prices as they fixed those shortage issues.
Check price/performance ratio of these CPU's.
I suggest go for 1700x or 2700x depending on needs and how often do you upgrade.
I would personaly go for 1700x since it is cheap and got simmilar multithread performance of i7-6900k that is plenty in my opinion.
But if upgrading rarely (more than 3 years) go for 2700x