Lighten the flywheel with caution. In the interests of not being hit by an exploding flywheel, make sure you leave a nice radius if every corner. A sharp inside corner WILL crack.

You can cut a fair bit away, but as the material gets thinner, the likelihood of cracks and fatigue increases.

It does give a top end gain, but to be honest, if it's a street bike then stick with the standard part for security.