http://cpu.userbenchmark.com/Compare...

100.- extra charge for 5% more power is not really worth it :/

If you are building a new system definitely have used it myself at a stable 5.2 GH/z.
but if you already have an 8700K in use then rather not as it is basically only a selected version of the 8700K. good cooling is also really necessary!

Best regards
Slipper

The i7-8700K is perfectly adequate and will be for a while, since the processor is often not as important as the GPU in games. With OC, the i7-7800K easily comes close to this one. Personally, I wouldn't need the performance boost of this processor and would rather save :)
However, this is also a limited edition, if that's what you're looking for... (or if you know that your processor is very stressed)