With the factory decklid being Fiberglass you can carve out your stock decklid or find another one to carve out and make it light enough that the weight savings from carbon fiber would be almost nill.
I sat down with the guys at carbonfibrefx in Surrey and looked into it. He showed me some of the hoods they make for the import tuner crowd and if they make them to be a full use item. Proper re-enforcements and such to be as strong as the stock fiberglass pieces the weight savings would only be about 10lbs total difference. 10lbs is the difference of a 1/4 tank of gas. It is not worth it especially considering the cost of the piece. I believe the price was going to be around $500. Sure it would look cool and be bragging rights to have it, but............
You can spend the money in other areas to get the car to go much faster for the money.
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85GT 5spd ,93 Eldorado 4.9 Dual O2 Custom Chip, Archie Clutch. Custom Exhaust. MSD Everything 245/50/16's Not Your Average 4.9 Capt Fiero Com --- My Over View Cadero Pics Yellow 88GT 5spd Stock.