Last week I had the new trani put in my car, and in went the JWT stage 1 clutch and a Stillen aluminum flywheel. With about 400 miles on the new parts, here's how it feels.
The clutch pedal feels similar to stock, perhaps a bit crisper. Certainly the performance seems to grab nicely. I haven't really hammered it, since the trani is breaking in, but I get a nice chirp off the line without trying and so far it gives me a confident feeling.
The new flywheel is around 5 lbs, minus the ring gear. That compares to about 14 for the stock one, so with ring gear (around 3 lbs) that's about a 50% reduction. In the first 2 gears, the car is definitely peppier. In higher gears I notice the pickup over 3k rpm, but really at freeway speeds the difference is negligible. In fact, the loss of flywheel inertia might negatively affect high speed low rpm torque. I was worried that driving in SF might be difficult because of the hills. It takes a bit more gas and babying the clutch, but not so much that I couldn't compensate after the first feel for it.
Bottom line, it might not be a mod for high speed fanatics, but it's a pretty good mod for autocrossers. In lower gears, the car really seems to leap. I think the Quaife differential will really help bring out some more of the positive qualities off the line (or, if I hadn't ordered one, the VLSD I could have put in instead of the stock transaxle).

 

umm ... what does the flywheel do?

 

RPM's build/decrease more quickly with a lighter flywheel. Lighter is better.