I did exactly what QBallz did and got the 2006 Sport GT with 2.3L engine and manual transmission. I am very pleased with it and would suggest that this kind of car is better suited with a manual transmission. Somehow, the auto transmission does not do the car justice - perhaps auto is better suited to a Corolla or a Civic.
Reards.
Marty

 

The problem is if you go with a lighter flywheel that makes the engine rev faster your going to make the car harder to start the car moving, and it's going to be harder to shift smoothly.

Much like everything else on a car there is a trade off between performance and comfort. Just my two cent.

 

If you are having acceleration problems you should visit your dealer and they can address it. Mazda 3's do not experience acceleration problems under normal conditions. Also, stating the mazda3 is a slow car check its 0-60 times, believe me...they are very fast for its class.