It’s impossible to know exactly how much traffic you will receive from a keyword position. First, the data is taken from Yahoo, so how do you translate that to Google? Second, the number of people that click on your link is dependent on what your title and description says. That said, I’ve seen usability studies that say the number 1 ranked site gets clicked about 35% of the time, down to the #10 ranked site being clicked 2-5% of the time.