You might want to read through the thread he linked, there is some discussion (although not to the point where I'd call it research) of matching the letter grades up to a salary range. I think one problem with getting solid research on it is that most people were lucky to be able to draft more than 1 player who they new the letter grade for, making it very difficult to get enough data points. If each person who participates can only provide one piece of data, you'd need a lot of people providing the letter grade and the starting salary to come up with good numbers.