I was actually thinking about something similar the other day, I came to the conclusion that if I ever found out I was adopted I wouldn't bother looking for my biological parent's at all (unless I was afraid I might go bald!). The people that brought you up are your real parents, the ones you love so there's really no point in complicating things. Especially if your bio mum has made it clear she want's no contact, I'd respect that and go on as if nothing ever happened
But waiting till you were 40 to tell you? How absolutely bizarre, may as well not have told you at all :P