Not sure, everyone is different. I drove my trans with 300 - 400 whp for a whole summer, without breaking it, or any of my stock axels. That trans had 114k miles on it, when I started. I beat the SHIT out of it, and it never broke. Derek broke his trans about a month ago, but he just put in a low mileage one. Its hell on the trans, but its stock, < 200 bucks for a new one, plentiful, and a 2 hour job to replace.
The SRT transmission is a little bit tougher, but you have to make a subframe to hold it, and its about 8 - 10 times the cost. You are better off just blasting through transmissions once a year or so, and spending the 200 to replace it.
–mark