I have the metric mechanic lightened steel flywheel, with the 228mm sachs sport clutch; I really like it, it's an excellent value...
It's about half the weight of the stock dual mass flywheel, and not only increases power to the wheels (less drivetrain loss) but also helps you get up into the M42's sweet spot a lot faster.
I think it's probably the fourth best mod for an m42 (chip, clutch stop + short shift kit, suspension, flywheel) and if you are changing you clutch anyway it's a must have.
while yer down there, I highly recommend a new slave cylinder also.