I have a 2013 Elise S (S3, 220hp) with the newer 2zr engine. I first put the 7 inch 2bular back box on it. It was fun when absolutely on it (ok for Anglesey and Silverstone trackdays), but it was very Tiresome on motorways etc.
i recently swapped to a full Larini system - 4-1 manifold, sport cat and group n (switchable) back box. Wow is all I can say. Worth every penny. Even on the loud setting (slightly louder than the 2bular) it doesn't become tiresome at all. The quiet setting is still quite loud, but I think it comes in at 98-100db at 50cm and 45 degrees, so should be ok for most tracks.
Personally, the Larini tone I prefer, but It isn't an entirely fair test as my Larini has extra help from the manifold and cat. The car also feels better/faster on the butt-dyno....
if you do go for 2bular, listen to the guy there and get the 8 inch.