I have been on and off a programmer over the last 10 years. and the last 3 have been using vim(only these 3 were on linux), used to be scite for the first 3 years and whatever was available the rest of the time (which was mostly part-time programming, was otherwise studying cog. sci). I have so far been against the mousing faster than keyboarding argument and even now i reach more easier for the keyboard.
But over the last year i have been writing and i can relate to that effect of interference caused by planning keystrokes in my writing(guess still am not enough of a programmer to notice it in writing code).
So i am beginning to understand that the question assumes a simplicity that plain and simple speed in some specific and narrow lab task is indicative of real-world problems and challenges. (Aka, problem analysis, solution space search, choice of solution, planning execution and then execution).Depending on the experimenter and the lab group he's working with, these experiments tend to focus on isolating one of these phenomena/mental processes(sometimes not even clear to the experimenter).
Anyway, at the moment i am convinced that writing is best done in blind manner, ie: no visual input, switched off monitor. I currently use a white on black bg on 750 words, but wish i could find a way to turn off monitor on my laptop and keep typing.
P.S: i found the same thing about QWERTY vs DVORAK Layout. i was a touch-typist(barely average) on QWERRTY too and all the research suggested it's not worth re-learning DVORAK. I started it off as an experiment(1 hr a day of DVORAK for 2 or 3 weeks) find that my writing stamina has improved. I'll bet that there are hand/palm size(area, angle,distance between fingers etc.) variations in the effect of KB layout and that's a statistically significant factor.