I read essentially this statement in the Howard Brody book, which BTW is essential for every Tennis geek. They say racket "power" and string tension makes makes no difference to pace of serve. I wanted to say this earlier when someone suggested Drakulie try a more powerful racket with lower tension. But I didn't say anything because it seemed (to me) to contradict with something else in the book. They say the serve speed will be pretty much equal to the racket speed is at point of contact. I have some issues with accepting this, because it implies that you should use a long, feather-light, stiff racket that you can whip through very fast.