Honestly this comes down to what you want to do with your car. Their is several options and if u have money their is basically endless options.
I would def. say go full bolts ons and get rid of any weight u can. For example if u dont use ur rear seats, lose them. Get a lighter battery, maybe some kind of race seats (depending on how serious u r), lighter trunk, wheels etc...All this should make ur car shed at least 150lbs, gain 60-80whp (depends on what products u use) and it will make the car feel a lot better all around. I went this route before my SC and the car felt great at the track. I also gave bolt on e60 M5s a good run. Hope this helped.