8500 sounds good for your situation. it's very tricky to determine what exactly is the best deal. i think the 2600x is a better all around cpu and game performance between the 2 should be extremely close. based on the lower clock speed on the 8500 and all the benchmarks i have seen on the 8600k, i bet the fps are neck and neck. the problem is how well will you perform with 2400mhz ram and can you oc it to 2933 or 3k? probably don't want to find all of these things out after you order online and potentially pay restocking fees to exchange..
the other side of this is that going ryzen would probably set you up for the future a bit better. you may buy new ram now, but with intel would have to buy a new motherboard earlier and basically offset the cost of the memory purchase you saved on initially? you could jump from ryzen 2 to 4 or 5. intel probably will change the socket after this 9th gen, but you could also use an 8500 for a few years save the money and build a intel 10th or whatever gen system with ddr5 memory, buying a new socket and memory standard all at once.
both cpu are good, you really can't go wrong. good luck