Intel Core i7-7700K was in games is better than Intel Core i7-7800X
In a resource Techspot was the new six-core processor Intel Core i7-7800X, which failed to compare in games with Quad-core model Intel Core i7-7700K. The result was not in favor of new items.
The difference in the frequencies (the base frequency of Core i7-7700K and i7-7800X is equal to 4.2 and 3.5 GHz increased to 4.5 and 4.0 GHz) were more important than the difference in the number of cores. This rule applies in the case of acceleration. In addition, Core i7-7700K consumes less electricity.
It remains to add that the Core i7-7700K has less cache second and third level (per core) than the Core i7-7800X, but in games it was not so important.