At 400+hp, What kills A904s?

I'm in Southern California. This is the horsepower capitol of the world. I got fools comin at me with 7-800 horse all the time; street cars.
I will rephrase that for you......you live in a liberal schithole and any COMPETENT trans builder would be recommending at a minimum a billet input shaft at those power levels for durability but since you make no mention of them you must be the secret sauce 99.95 out the door 904 will live at all power levels builder. I will stick with Pro Trans and enjoy running more power than that with ZERO issues.