All of the problems you have had really have nothing to do with "speed". You car may run smoother now or seem a bit more linear in how the engine goes about its business...but you most likely will not feel any more "power" after replacing what you have replaced. Boxsters are not "fast" in the sense you are trying to achieve. Especially your model. They are meant to be wholly enjoyed!
PS--DO NOT fall into the "performance upgrade" hole. LOTS of money for little, if any, performance gains with these cars. While some on this board disagree and love to spend huge sums of money on small performance gains, I believe you would be better off saving that money and buying the best car you can and go from there. Good Luck!
