Teppo :
CTurbo :
The i7 6700k will work in any motherboard that the i5 6400 works in so there is no issue there. What motherboard do you have? The i7 6700 (non K) may be the better option.
Im not sure what motherboard i have since its a pre built system and the only thing ive had changed was the power and gpu, anyway for me to find out without opening up my pc ?
Install HW monitor, it will show a good amount of your hardware specs and temperature.
The 6400 isn't a bad CPU, so before you change it, check the CPU clock/load and temperature when you run your video editing software or games. Something like MSI Afterburner will display CPU and GPU speed, temperature. If you find the CPU running at 100% a lot and causing gameplay to stutter , then you may want to upgrade the CPU. With video editing, it's more of a matter of how much time you are willing to wait for the processing to complete. If an i7 6700k does a clip in 30 seconds, and the 6400 takes 50 seconds, it's not a whole lot of time to wait, but if you process very large videos or batch process many clips, then those could be a few hours extra. On the other hand, it may be the GPU that is the limiting factor.
Even if your motherboard doesn't support overclocking, I'd suggest you buy the i7 6700K anyway if you are find with the price premium, since it runs 4.0Ghz peak clock against the 3.4GHz for the 6700. You won't get the overclocking benefit of the unlocked multiplier, but if your video editing demands that high, the extra core speed may be handy.