Adam,
You mentioned that the main reason for the typing delay is because CE is cleaning the HTML code as the user types.
Why not consider this another way: Provide an option to use CE strictly as a text editor and when this option is set true, don't do any such cleaning or other actions on keydown that might delay the typing from appearing. For example, call it UseAsTextEditor.
I assume that some of your customers buy CE so that their users can develop web pages, but I would suspect most of us buy it to use as a sophisticated text editor (at least that's why we bought it).
In the last couple days, we have tried several of the competitive products and they don't have typing delays in either IE or FF, and all of them also have an HTML mode, so they must be doing less than CE is doing. Maybe if CE's new property - UseAsTextEditor - is set true, CE would only do the minimum on keydown, so that there would be no typing delays.
We want to continue with CE because it is a superior product in many, many ways, but we have to resolve this issue in order to move ahead.
FredD