r5 2600 vs i5 8600k

Solution
Most assuredly the 8600K would give you higher framerates, usually (see below). However, this comparison is a bit... off. The 2600, while still not beating it in framerates, is supposed to compare more closely with the i5 8400. The 2600X is supposed to compare to the i5 8600k. That said, if you aren't overclocking, go with the i5 8400 or 8500 for a more reasonable price.

Now for the beautifully rendered 4k elephant in the room... at 4K the CPU doesn't matter much. Well, it does matter, but you are graphically restricted at 4k. Your video card will max out before your CPU will, so anything over an i5 4th gen will score nearly identical framerates given the game. If we both had GTX Titan XPs and I had my i5 4590 and you had an 8600K, the...
Most assuredly the 8600K would give you higher framerates, usually (see below). However, this comparison is a bit... off. The 2600, while still not beating it in framerates, is supposed to compare more closely with the i5 8400. The 2600X is supposed to compare to the i5 8600k. That said, if you aren't overclocking, go with the i5 8400 or 8500 for a more reasonable price.

Now for the beautifully rendered 4k elephant in the room... at 4K the CPU doesn't matter much. Well, it does matter, but you are graphically restricted at 4k. Your video card will max out before your CPU will, so anything over an i5 4th gen will score nearly identical framerates given the game. If we both had GTX Titan XPs and I had my i5 4590 and you had an 8600K, the difference would be within margin of error. It is the same between the 2600 and the 8600K. There is a 2-3 FPS difference across the vast majority of games. So, the 8600K will give you ever so slightly better performance, but I dare ANYONE to try and spot the difference.
 
Solution
It comes down to how many threads your games can effectively use.
12 for 2600, 6 for 8600K
The types of games that can use more than 4 threads are typically multiplayer games.
For those, the 2600 might be best.

Most others depend on the single master thread for performance.
For those, the 8600K is better.
The top overclocks for the 2600 are in the 4.0 area, the top overclocks for 8600K are more like 4.9

If you have a top end card like the GTX1080ti, why not spend $120 more for a 12 thread I7-8700K and get the very best.
 
Personally would go Ryzen. Pretty much the same performance at 4K with more threads for other workloads or even things like streaming or just doing 5 things at once. On top of that Intel will probably kill off LGA 1151 or at least chipset compatibility when they get 10nm down and meaningful upgrades per core happen. Ryzen 2 (7nm) will most likely work with the same board as the 2600x
 


Spend 120 more for 1 FPS and a dead platform. Great return on investment there.
 


How is it a dead platform? Just because Intel will likely change the socket?

Chances are by the time you need to upgrade the ryzen cpu you would probably want a new motherboard anyway for new features.
 


Don't get me wrong, I'm pretty much an AMD fanboy, but this comment strikes me as somewhere between rabid fanboyism and ignorant. The Intel 300 series platform is far from dead. It is just getting started and will be supported for a while longer. While AMD is better in this respect, it will only be around 2 years till AMD moves on to AM4+ or something. Last year the support out to 2020 was a great feature, this year it was a good feature, and next year no one will care because it will only be a year till it is replaced.

On top of that, the 8700k should turn out to be a good return on investment as it will be a relevant chip for a long time. Considering how well the 2600k still works and how long it has been around, you can expect years of use out of the 8700k. It is foolish to look at the upgrade path exclusively while ignoring the fact that CPUs don't just stop performing when a new chip is released.

Will Ryzen turn out to be a better investment? Who knows? You pretty much need a crystal ball. It is a great CPU, and has better value than Intel's offerings, but it isn't the best. For gaming the 8700k is better, in the vast majority of benchmarks. Heck, the 7700k which is sitting on a "dead platform" is still highly competitive in gaming. It's platform support doesn't affect its performance and it will still be a good CPU for a good number of years, there just happens to be better things out nowadays. That doesn't make them a poor investment... what makes them a poor investment is that the 8700k and 2700X exist at the same price point.

Your return on investment is always the performance vs price and the time you find it useful. If you get an 8700k and hold onto it for 5 or more years, that is a good return. If you want to upgrade next year to the 9700k, that is a poor return. Those people upgrading from the 1700, 1700x, or 1800x to the 2700x are getting a poor return on that older hardware. Those CPUs might not be the top dogs anymore, but they still perform well and have a lot of life left to them.

Upgrade path plays into value, but it does not determine value.