Well with $600, we can go with something like this:
System Builder
9600K has 6C/6T and I added a cooler since the CPU doesn't come with one. Alternatively, you can switch the GPU for a 5600XT and still be under $600 (5700 is too much
).
Gigabyte Radeon RX 5600 XT 6 GB WINDFORCE OC Video Card
Gigabyte Radeon RX 5600 XT 6 GB GAMING OC Video Card
Also,
the motherboard isn't capable of overclocking so you won't be able to OC that 9600k. I've picked that mobo because it is affordable while being good quality and to fit the budget. If you do plan to OC the CPU in a near future, then we'll have to find something else but expect more $$$.
There are other configurations to explore (maybe an i7 9700K to have 8 cores?). In the meantime, here are some benchmarks to give you some idea.
Ultra settings with i5 9400F (6C/6T @ 2.9GHz)
High/Very high settings with R5 2600 (6C/12T @ 3.4GHz)
Ultra settings with i7 8700K (6C/12T @ 3.7GHz)