Interesting about your wheels... I think maybe my car will be like yours when done.
My motor should be up to 500Hp, have 3.9 diff and 18" wheels. I guess the power curve and your road / track usage conditions comes into play here.
First question:
What are your motor and rear tyre specs ?,

I am concerned at how long the T5 will last hence this thread, budget overrun years ago...
Second question:
Did you upgrade the T5 gear set ?