I don't know, I never learned proper touch typing, but I went from 100 WPM to 80 when I learned to touch type on the ortho keyboard. You're right that there's less movement, but I find it a bit less... convenient.
i'm definitely not as fast as i used to be (somewhere around 120 wpm as a non-touch-typist) after 2 years of typing on an ortholinear keyboard, but I don't really mind. I'm much more comfortable and my fingers don't hurt as much.
I went from ~110 pb, 100 average (on common word typing tests) on row-staggered QWERTY with an untrained hunt-and-peck to ~105 pb, 100 average (on common word typing tests) with Dvorak layout on an ortholinear keyboard.
I'd already spent the time to learn Dvorak layout on row-staggered keyboards. Having had that training, picking up an ortho was straightforward. (Although my average wpm on typing tests after picking up the board would've been ~90).
I suspect if all your fingers 'know' is where the keys are (rather than following discipline of 'column per finger'), then adjusting to ortholinear would be harder.