I don't know what you mean by "high frequency". But I can tell you it has enough throughput to manage hi-dpi mices and wiimotes. I don't think keyboards will cause trouble. I cannot really tell, I never had any trouble with them and I can guarantee you I have bashed my keyboards as fast as humanly possible.
I want to make a game that allowing high frequency input with keyboard, I don't know if raw input can handle that.
Keep in mind that many keyboards cannot read many buttons at the same time because of an hardware limitation.
If you find that useful, do you mind rating up messages? Hopefully this will also help other people in pinpointing information with ease.