Turbo's are so much better designed today that a single turbo that is capable of supplying enough cfm for over 500 whp in a 2.0 liter 4 cylinder engine with virtually no lag with the aid of proper electronics. So that being said it has nothing to do with outright power but rather a package that is affordable to a broad base market also considering operational cost to the consumer including insurance and maintenance. I think Mazda made a good choice in going with this package. It gives some that would buy a Audi, Jaguar etc. a cost effective alternative.
Ok, enough with the blah, blah, blah...... after market turbo kit for the 3 such as Highboost is the most cost effective choice at the moment apart from going custom. We have a kit for the MZ3 coming out in the near future so that would also be an option. So far we have made VERY, VERY GOOD numbers and reliability is also inline.