Matt Garrioch did a study of drafts from '87(I think) to '01 on every player drafted. He found that, in the first round at least, HS RHP were slightly more likely to be solid everyday players than college RHP. However, HS LHP failed at a very high rate, something like only 20% made it to the majors. Here is the link to the google docs spreadsheet. You can look at the success rates of all the positions broken down by HS/College, RH/LH, Round drated and differentiated into never made it to majors, part time player, solid regular, part time allstar, regular allstar, superstar, alltime great. He used WAR as his stat of choice. https://docs.google.com/file/d/0B-772wlhxPhPNjUyY2JiMmItYzJlYi00Yjk5LThlOTUtODkwN2IzMTU5ODIx/edit?hl=en_US