Remember to look at both the sending element and the receiving element characteristics. The receiving element on the KOP board is the Vishay TSOP34838. I found the Vishay datasheet and Figure 11. Relative Spectral Sensitivity vs. Wavelength shows sensitivity from the range of 750 to 1150 nm.
It is greater than 50% from 825 to 1075 nm and peaks around 950 nm. Therefore, your selection of sending element frequency will tend to have minimum impact on the system design because the receiving element has a wide range of sensitivity. I will attempt to attach some pdf's for your reference.
