FWIW, I fitted my new 6kg Cusco Cromoly flywheel today on my JDM STI7 RA. Initial impressions are that while being noticably lighter than standard, it is not as light as my old MY00 JUN Cromoly flywheel (think it was just below 5kg).

This Cusco item lets the revs pick up and fall faster, and is still as easy to use in stop-go situations with the standard clutch (which BTW, 34000kms of moderate driving still looks pretty good). There is also no problem with idling - smooth and steady as before.

To anyone who's interested in a lighter flywheel, I would say that this 6kg Cusco item gives quite a moderate lightening. The 7.2kg STI one apparently has a very stock feel, and IMHO drives too "standard" to justify the expenditure.

Hope this helps anyone contemplating a new flywheel on the STI7.
Cheers.