Moving Rear back or Cut front part of wheel well

I am trying to get the tallest and widest tire on the duster. I am in the beginning stages of moving the springs in and have the chance to move the rear back instead of trimming, but if doing both will allow for an even taller tire, I will do it. So the question is, how tall of a tire can I go if the wheel is tucked in, Mini tub, springs relocated and rear moved back. Thanks!