Billy sports are harsh and uncomfortable.
Hot Air intake is a waste of money and in some cases lower HP.
Any exhaust upgrade is for sound changes only (and to empty your wallet of money)
MarkD chip (or any other) is the best bang for the buck. LSD and a better ratio will make a "seat of the pants" difference.
Bottom line is your M60 is pretty well designed for efficient power. Ensure it is running well (as Nick_V mentions) and enjoy. The only substantial path to increased power is a SC system which is not cheap.
89 535iA ; 93 M5