Sports cat help ( advice)

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Hi I am wanting to change my standard downpipe to a sports cat ,but not sure whether to get a 100 cell or a 200 cell ,I would want the car to pass mot without any probs each year , I am getting my car remapped soon ,and was wondering how restrictive the standard downpipe really is ,been looking at scoobyworlds ninja decat , and cobra. Car is a 1997 wrx thanks

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Thanks scoobiewrx will the 200 cell make much a difference over standard down pipe