Few games can effectively use more than 2-3 threads.
For gaming, 6 threads vs. 12 threads is not that important.
Both chips will turbo to 4.6 so that is a wash.
If you will buy a Z390 based motherboard, it makes sense to buy the i5-9600k.
Overclocking a K processor is a bit misunderstood.
Intel makes the K chips to be overclocked.
They guarantee a minimum level of performance, but the maximum performance can not be guaranteed.
It depends on luck in getting a good chip as well as the adequacy of the cooling system.
The overclocking is as easy as increasing the default multiplier of 37 to a higher number. Perhaps 50 on a good chip.
All other settings can be left at default for conservative overclocks.
What I am saying is that by not permitting an overclock, you are leaving some 30% single thread performance on the table.
Single thread performance is what most games need .
On ram, intel performance is not particularly sensitive to ram speed.
3000 is fine.
Fancy heat spreaders like the g.skil Z chips are mostly marketing.
To be sold at a price premium.
Ram does not need such heat spreaders at all unless you are a ram overclocker.