The higher clock speed will help a bit, it is 3.4GHz vs 4GHz.

If rendering and no gaming, then go for a faster CPU, not all software use GPU as hardware accelerator so it might end up with zero usage at all.

If you go for i7 6700K and would like to overclock, you need Z170 and aftermarket cooler, this increases the total cost.

And if possible, go for a faster memory (> 3000MHz), it does help speed up the whole operation speed, but it comes with a cost as well, so in conclusion, if budget is tight, go for non-overclock build, it is just slightly slower than overclock build but you can save a lot of money and time (no need to spend time to adjust overclock settings).

Running Z170 but with DDR3 RAM? Because the RAM you listed is 1600MHz which is a DDR3 module speed, DDR4 starts with 2133MHz as base clock.

i7 6700 base clock is 3.4GHz with turbo speed of 4.0GHz and 3.7-3.8GHz when all cores are being utilized, the turbo speed is enabled by default in BIOS (normal case), the system will automatically boost the speed when needed, just make sure your power options is not set to "power saving mode".