How much time will you be spending on Streaming or any video/photo editing?
Even though the 2700X is not as fast for games as the 8600K, it is a tad better for most of the other tasks you want to throw at it.
To highlight the strengths of each (in my eyes):
** 2700X:
PROs
- Lots of threads to run a lot of things at once.
- Performs decently enough to not notice a massive difference with the 8600K in games.
- Bundled cooling solution is really good, so you don't need to get a cooler.
- A great amount of cheap alternatives for Motherboards.
CONs
- Needs fast RAM to really shine.
- Depends a lot on the cooling (case included) so it performs decently (Turbo speeds).
- You need to do a bit of reading on RAM support so you buy the correct ones (supported).
- It is power hungry when pushed, so you need a decent PSU so it can keep up.
** 8600K:
PROs
- OC's really good.
- Easy to keep it cool at stock with a cheap cooling solution (as in, you don't need to spend on liquid cooling or a huge HSF).
- At stock performs really well on games and OC increases that advantage by a noticeable margin.
- You can use mainstream RAM without fear. Keep in mind it will still depend a bit on RAM speed, but not as badly as AMD CPUs.
CONs
- For the K version, if you want to OC, you're stuck with Z Motherboards; they can be a tad more expensive that what you'd like them to.
- Doesn't come with a cooler (unless they changed it recently).
- Temperatures ramp up really quickly when doing OC, so if you're planning on OC'ing it, you will need to invest in decent cooling (think CM Hyper 212 and up).
- If you're doing OC, it can also be quite power hungry, so same as the 2700X: it will need a good PSU.
I hope that helps!
Cheers!