A much discussed topic, a decision deserving of careful thought, a conversion involving considerable cost.
Transmission rattle is caused by impulse generated when a cylinder fires. It is absorbed by the DMF so long as the engine is essentially stock and in good tune. This goes for both early & late gear styles in the ZF transmission. The difference in gear styles, straight vs helical, becomes apparent when the conversion to a lightweight, SMF is made. Even the later style, helical gear design develops rattle, but to a lesser degree.
A light weight transmits more impulse to the transmission than a heavy flywheel. A heavier flywheel also makes street driving from a stop easier.
There are alternatives to making the giant leap from the stock DMF @ 37.5lbs to the Fidanza @ 13.5lbs.
Jerrys Gaskets makes an 18lb & a 22lb billet aluminum flywheel with a replaceable, steel clutch surface. Both flywheels have the same dimensions as the stock DMF. This feature maintains the same clutch geometry when using the stock pull-release clutch system.
https://www.jerrysgaskets.com/flywhe...et-90-95-28c1/
https://www.jerrysgaskets.com/flywhe...et-90-95-28c3/
The next obvious question is how much is the noise reduced when compared to the the extreme, lightweight flywheels, like the Fidanza and its counterparts. The answer is subjective and depends on the other variables, tune, cams, transmission gear style, etc.
There is no way to answer, except the lighter the flywheel, the more impulse transmitted to the transmission, i.e. more rattle.
In closing, "rattle" is at its greatest when the transmission is in neutral and the clutch is engaged (pedal released). Some drivers always shift to neutral & release the clutch pedal at stoplights....... other do not. If you do the former and it embarrasses you when others are nearby, then maybe you switch to the later.
There is always going to be some gain & some loss in the conversion. "Choose wisely grasshopper".