http://www.fangraphs.com/blogs/how-much-extra-credit-should-we-give-a-lefty-starter/
"Left-handed starters: 90.6 mph average fastball, 20.3% K, 7.1% BB
So if Escobar could sit over 91 mph as a starter, his velocity would indeed be above-average for a lefty starter. Of course it’s an issue of supply, as only 30% of the sample was left-handed. That means fewer 95 mph guys, fewer Danny Salazars, fewer chances at big velocity."