Everyone needs more Hp right? Unless you drag race or road race (and with this mod it would be illegal in most superstock or superbike classes) you don't really need that much more power. And if you did happen to track day or roadrace spend the money on suspension upgrades and riding lessons before you need more power.
The ZX7 if I remember correctly puts about 115 hp to the rear wheel. The ZX9 was up to about 127. You shoudl be able to pipe, jet kit, air filter, overbore, head/ piston work into the same range...if not more. All for cheaper unless you just happen to have a wrecked 9 layin' about.