As in subject heading, a lightened flywheel is a must! I had a VR clutch and the flywheel swapped last week and have been driving over the weekend, it's simply fantastic. Something VW should have done to the mk3 out of the box.
Some things I've noticed since getting it done:
Acceleration greatly improved, feels like I've knocked a second off my 0-60 time (if I were ever to do one) The car just urges itself on now and revs extremely freely, not like the big slow arc of the rev counter I had before.
MPG seems to be alot more stable and doesnt fluctuate nearly as much when I plant it. All down to fly weight and inertia, needing less energy and thus fuel to spin it up, and as it loses inertia quicker it needs a slight more pressure on the throttle to keep it at a constant speed when cruising. However because there is no longer such a big dip when accelerating out of the blocks I can see the overall benefits outweighing the small downside of tiny bit more pedal pressure to maintain motorway speeds.
Downsides if these can be called as such - You have to get used to and relearn moving off from a standstill as it will love to stall if you're not hot on it. This disappears after a few miles and it becomes second nature. When cruising at 30mph, Its better to be in 4th gear instead of the 5th gear I used to be in, otherwise it bogs itself down more easily, but not even an issue.
Overall, do it, it's an awesome mod, cheap to do and with real world effects felt after doing it, not like the whole stainless exhaust and filter mod.. you can really feel it!
As an aside, guy called Hotgolf on clubgti did mine, top man!