Whoa, you have a lot of research to do. Those are two examples of different turbo sizes, the size of the turbo mostly relates it's efficiency to the engine you use it on. The wastegate controls the actual boost output of the turbo, however a small turbine looses efficiency faster then a larger one depending on engine displacement and volumetric efficiency blah blah blah...

Before you decide to turbo or build the engine for turbo, you really need to decide what kit or what parts you plan to use. Save up your money, and while you are doing that take time to learn how a turbo and components work, and you'll be much better off when it comes time to build.

That said, a set of aftermarket rods and low compression pistons never hurt anyone.