If writing words by hand is too slow for your mind, you're not thinking hard enough. The speed of touch-typing approaches the speed of cognition, but deep analytical and creative thought is much slower than even the slowest forms of committing information to a medium (eg. engraving a stone tablet).
The "speed of cognition" I'd imagine is mainly limited by the fact that most people say (in their mind) what they read/write as they go along and we can only speak so fast. With writing we are also limited by our fingers but reading can go much faster if one learns to get rid of the inner voice (speed reading).
And even though I agree with you that touch-typing isn't that much of a limiting factor when compared to the time required to come up with something sensible but unfortunately, at least for me, those deep analytical and creative thoughts doesn't produce a steady stream of characters but rather bursts of sentences and paragraphs and taking the time to writing them out obstructs the thought process (depending on what I'm doing (most of what I do isn't that challenging)). So I'd say that the speed improvements of touch-typing compared to handwriting can be quite useful (and being able to get rid of it entirely by taking 'snapshots' of a current thought process, continue, and then later go back and summarize and formulate all snapshots would be awesome).
