Flywheel weight &/or moment of inertia
 

So I've just acquired a slightly used Rx8. The dealership tells me, IIRC the numbers correctly, they can supply & will install a MazdaSpeed "light weight" flywheel for @ $620 in parts and something like $750 or so labor. On a motor that seems happiest regularly reving from 3k to almost 9,000 this seems like it might be a good idea, but I'm wondering about some of the details.

A couple or questions. Can anyone point me to the stock flywheel/clutch assembly stock weights?

Is/are there any moment of inertia figures or data available for the stock parts?

How about for the MazdaSpeed flywheel? Weight &/or moment of inertia data?

Last, any end user reports on observed performance benefits? Gas mileage increase? Lower ET?

Thanks
Mike ~ Colorado