Coilovers will drop weight along with wheels, rotors and calipers. A good titanium single exhaust weighs about 10lbs (cat back). Headers and loss of cats will save weight. Smaller battery, seats....all help.
How serious are you? Is it street use or track use?

 

It was Sport Compact Car's build. I probably have the magazine tucked away somewhere.

I drive the car in town once in a while, including to and from the track. It has to be able to handle long drives, as tracks range from 3.5 to 12 hour road trips. My Z has a hitch and a trailer to carry tires and tools. I don't want to lower it any more. The Koni shocks and RSR springs have a well-balanced setup for street/track and I don't want to mess with perfection there. Coilovers are definitely lighter. I'm leaning towards a Vortech with a mild pulley as a result of this thread. That way I can add a roll bar and safety stuff, and go conservative on the tune. Living at high altitude (3000+ feet) I can probably get around 330 HP.

 

I've shreded everything out of my Z, it sits just south of 2800 pounds and dynoed 257 WHP. I'm still on a stock motor and stock sheet metal. There is a cat in St. Louis that is going to make a dry carbon hatch without a window cutout (i can't see through mine anyway) and that should ring the scales at 4 pounds. Depending on his results, I might commision him to also do doors.

I currently have a kirk 4 pt bar, but I'm looking at cages now. This winter may include cams, so I'm fairly cloe to what you are looking for, howevre you get classed rather unfavorably with no dash and no interior.