I have a Magnex on my Cup. Nice beefy sound, not in the least bit offensive for the neighbours. If you have the windows up, you can feel the noise in your chest at about 3500-4000rpm
I reckon theres a performance increase in the low-mid range as the hit between 5000-7000rpm doesnt seem as big as before, but the car pulls better from lower down. I have a Green panel filter to, and can recommend this combo. Quality of the Magnex is superb and the car is very smooth and powerful.