TO be honest, I had my flywheel lightened by about 10-15% and balanced with the entire bottom end on my 370BHP saff, and it was absolutly superb, reved nicely and was really torquey and easy to drive. When My clutch died I took a while to replace it ( cos I am a lazy bastard ), so when I got round to doing it I had to have the flywheel re-faced to clean it up, and the extra weight that got taken off really made a difference, it turned the car into a bit of a pain in the arse as it was much harder to pull away smoothly and lost a fair bit of low down grunt.

IMHO if you are using it for a road car then only go slightly lighter (15% max) and balanced, and it will be superb. Anymore and the trade-offs for revability will loose out to ease of use.