I am leaning towards a 94-95 e36 318i / is, reason being it is less electronic crap ( EWS, trac control etc. ), OBD I and convert from OBD II to I would be illegal with a Z3, the 318ti has a crappy rear suspension setup and slightly less favorable f/r weight. I think the 318is would be ideal, it has decent aero, cheap body panels, the 325's brakes and suspension, and is well supported with aftermarket goodies (chassis wise), and if a map can be created for the FI it would be a little less hassle with OBD I which should still be a early motronic chip. Andy's suggestion of OEM header extrude honed and coated sounds interesting but my guess is more to be gained by simple cat delete and free flow pipe to a simple race muffler to keep a touch of back pressure. I wil post at BF to see if anybody has any experience with supersprint on a M42 / 44 and will keep IT.com posted.