You *really* need to do a lot of reading and research on your own before you invest in a pile of crap turbo that you'll never want to use on your truck. You keep referring to how much boost you want to run... this should *NOT* be the basis on what you're looking for in a turbo. As someone stated before, 12psi on turbo A, turbo B, and blower C can yield all sorts of different powerbands, numbers, and violent results. Go on forums made for your truck, do some research, and learn about turbos in general before taking an expensive stab in the dark.

Oh... and you're question about what's big and what's small is all relative to who you're asking and your application. Your typical =>2.0L 4cylinder guy may consider a 53mm GT30R to be "huge" where as another guy with the same car would consider it tiny. Also, there's MANY MANY MANY more factors on what makes a turbo "big" aside from the sizes of their housings.