I'm a lefty myself. I've noticed that I also use my left hand a lot more in common words and think that seriously does give an advantage on qwerty.
I've never really "trained" until lately when I realized I was fast. I didn't even know I typed fast until college. I had a professor a couple semesters back who made us take a typing test at typingtest.com and I had 108WPM. I was like, is that good? while everyone else was around 20-40WPM. The girl next to me said, "Holy ****!" So yeah, since then though I've been taking typing tests regularly and buying mechanical keyboards in hopes of impressing girls. It pays off too, I'm typically at 120WPM these days when I'm fresh. Unfortunately that probably just makes me look even more pathetic. I mean, what an uncool skill to have eh?
Man, we were graded on a 100 scale for that test too. So if you had 38WPM, like the girl next to me, you got a 38! What a harsh professor. Since we used typingtest.com though, I changed her URL. Typingtest.com's test apparently follows the honor code lol. You can change it to whatever you want... so she got a good grade, har har.
DO I GET A 9218 OUT OF 100, PROFESSOR? A+++++++++++++++++??? No, we only changed it to like 90 or something so as not to raise suspicion, but yeah typingtest.com's results are like penis sizes on the internet. Speaking of which, you think that girl would have done something to mine after... y'know, saving her grade and all... but no such luck. ;(