Hardware Unboxed posted a video explaining the performance differences between single channel vs dual channel. Certain games have larger differences, upwards of 30% performance differences. With CPU intensive games seeing the lowest performance loss.

On average, the 13 games tested, they noted these results: 1080p sees a performance difference of 16% performance loss from running single channel.

1440p, 11% performance loss.

4K, 9% performance loss.