heh, trim is the pitch (angle) of the wheel's. it is determined by the size of the inducer and the size of the exducer aka the small part of the turbine wheel and the large part.

just throwing it out there, but you could have a 60 trim t25, and a 60 trim t88, trim is not the size of the turbo, it's the angle that the turbine blades are.

turbo size depends on what your hp goals are, and hp goals are usually dependant upon how much money you have for the turbo as well as other necessary parts needed to support that particular HP reliably.

give Mainstream Performance (678-567-9384) a call and they can help you

good luck with it,
Dave =]