Thats an incredibly open ended questions, turbos made for higher boost will give more peak HP but with longer spool times, while a smaller, lower boost turbo will spool faster and hit boost quicker with lower HP numbers... this is a gross generalization ofcourse, there are any number of turbos and custom turbos out there for every purpose under the sun.
It really depends on what your wanting to spend. With a low boost setup, on alot of engines people will run stock internals, stock head gasket and only fuel mods, and maybe an intercooler. With a high boost setup, youre gonna need to get some head studs, and a better head gasket than stock, and maybe even build your bottom end. and your definately going to need an intercooler.
