This isn't related to keyboard layouts specifically, but is a general typing question. Do you sound out words as you type them, or do you spell out words letter by letter? While switching from QWERTY (80wpm+) DVORAK (yes I know this is a Colemak forum, they don't have any good forums so I lurk here instead), I've realized that I can now copy text at about 40WPM, but actually typing my own thoughts is a lot slower than that. While taking a typing test with both layouts, I noticed a very distinct difference in my thinking when taking them.
In QWERTY, I type almost entirely what I would call phonetically. I don't consciously think about spelling at all, and I sound out the word in my head as I type it. Complicated words that I don't know how to spell slow down my speed a lot, while simple words increase it. In DVORAK, I find myself naturally spelling out words letter by letter as I type. This made me think about the people I see on these forums that hit a barrier around 40-50WPM. I could easily see this as being an upper limit if you're thinking about each letter/finger role and not getting to the point where it becomes unconscious when you think of the words.
So, a little survey for my theory, how fast do you type? What do you think about when typing (spell things out or just unconsciously spell)? Do you type significantly slower on words you're not sure how to spell or random text?