It appears that the Superhawk is a difficult beast to get much more power out of, cost wise. I have a riding buddy that has Web cams, KW springs, big bore/high comp. pistons, HRC ignition box, air box mods, full exhaust, Etc.. According to the dyno, he gained 12.8 HP! at a cost of over $3k in parts alone, when all was said and done. After switching bikes on a ride, we both preferred my bike. Hawks jetting guidelines, Erik's lightened flywheel, 16/43 gearing, Jaimie's suspension upgrades, SS brake lines, HH pads, etc.. Sure, he has more top end power, but the power is way up there. not really streetable. Now he gets maybe, 90 miles from of his 19 liter tank! It all depends on what you're trying to accomplish.
For me the most noticeable engine mod was the flywheel.