I switched to dvorak 3 or 4 years ago after 15 or so years of touch typing on qwerty.  At the time I switched I could type ~120 wpm with qwerty.  It took very little time to get up to 60-70 wpm on dvorak.  Now, after 3-4 years on dvorak, I can type 90-100 wpm.  So my advice is similar to others here.  Don't switch for speed.  I have never had RSI problems, so I can't comment on that aspect.