This question has been debated a million times. It all depends on what you wanna do. How much money are you willing to spend? It is true that there arent many aftermarket options for the zc, but if you look hard enough you can find whatever you need. Seeing that you have a SI already I would get the ZC and use your SI tranny. For the price of a b16 swap you can get a zc with i/h/e, pg7 ecu, and some kind of reground cams, like crower, and you will be puttin down anwhere from 125-135 hp which is close to b16 hp and you will have tons more low end torque. Depending on how well you manage money, you could get a zc with a t25 turbo setup which would put down between 175-190 hp. But if you are going for all out power, get the B16. It can put out over 250 hp with most turbo applications. It all depends on what kinda money you wanna spend.