Here's some food for thought on rotational inertia:
http://www.tiltonracing.com/content.php?page=faq&view=3
From that page:"Doubling the weight of an object without changing how far the weight (technically mass) is from the axis of rotation doubles the MOI, which follows common sense. Doubling how far the weight is from the axis of rotation quadruples the MOI,"
BTW, I just started using a 7.25 twin disc with Tilton cerametallic discs. It weighs over 20 lbs less than the previous 10.5 street twin setup and that weight is on a smaller radius. Whew!, what a difference. It's a treat to match rpm's during shifting and it revs quickly. The cerametalic discs are much thicker than the ones normally used on small racing clutches, they can therefore absorb more heat and slip well.