I had a 91 Mustang with a T5z in it. While it was a good trans it didn't hold well to much abuse. My Mustang made just shy of 300HP to the tires and weighed 3200lbs with me in it. I broke 3rd gear a few times and once I started to go easy on the 2-3 shift the input gear started breaking, I also broke 5th gear but that was just a snap ring that broke and was a 10 cent fix.

I did beat on the thing but it wasn't that much power, and not that much weight so if you plan to do any spirited driving go easy on the 2-3 shift and keep a stockish clutch in it to help take some shock off of it.

If this is a road course or autocross deal I am sure it will last a good amount. But if you plan to really jam gears learn how to rebuilt it.