Well, you would get it sooner than those who only pre-ordered it since having beta-access means testing the game and giving feedback as it's developed. As for whether some beta-testers would get access sooner than others, I don't think that's how it works. Since we're pledging to have access to early versions of the game to provide feedback & test things, it would be pretty inefficient to release these test versions of the game at different times to different people (￣∇￣")
If you were to pledge more than $45, you get a digital fanbook as well if you pledge $60, and the next jump is to $100 for all of that plus some physical merchandise (and further pledge amounts will net increased rewards if they hit certain target amounts). But no, I don't think you get any added benefit if you pledge, say, $50 instead of $45.