BMW M325i

I recently bought a legitimate 1990 BMW M325i in pretty mint condition. I recently chipped it, removed the catalytic converter, and installed a K&N air filter. The car goes well enough with these mod’s – but boys will be boys and so I am interested in finding out a little more about what I could do to improve performance more so. People have mentioned Shrick Cams etc.... Please offer some feedback/suggestions on what you think here or feel free to suggest some experts I can talk to in NZ?