depends on the airfilter. I've got a sports cat, stealth system and viper on my 1.2 and its much nippier. what type of air filter were you thinking of, closed or open? As for noise the viper gave a nice noise to the exhaust even when it has a standard one.
As for exhausts consider the quality carefully, i assume your from france by your name so not sure what sort u can get over there? Stick with a make with a good reputation, or get a custom one made up by someone like prospeed (a company here in wales) equivelent in france.