12700 is faster in pretty much everything compared to a 12600k, games or production. The 12600k has only one advantage, (if you want to call it an advantage) and that's the ability to OC.
Once you do OC it, you'll be up around the 12700 level in gaming, and maybe close in production, depending on the software. Some software responds well to higher clocks and IPC, some responds better to thread count.
All in all, the 12600k was semi-useless, the 12400 was almost as fast and almost as capable and the 12700 was overall better for the same cost.
Using software with a gpu render, the cpu isn't used much, so you can still do other office work or websurf with no/little delay or affects to the render since it's in the gpu. Using software with a cpu render, it can easily absorb every thread, leaving little to no room for any other use, and any attempts at such run the risk of contamination to the render.
So yes, even a 12700 can run slower in a cpu render, but it's going to take less time than a 12600k would, especially if it's a thread count type software, the extra 4 threads will make an overall difference.