[Noah930]

If you turn off the engine using your key, you'll lose your power brakes, but you're correct in the brakes will still kinda work. However, you will lose your steering. Not just the power portion, but likely the steering lock will activate (as in your moment of panic you'll probably turn the key ALL the way off, and not just to the first detente) and as soon as you turn the wheel more than a few degrees off center, it'll engage and you'll be stuck with the wheel in that position.

Still, better to have crappy brakes and possibly no steering (as long as you're pointed straight to begin with) as long as the car is no longer accelerating at full throttle.

Other option (probably the smarter one) is to throw the automatic transmission in neutral. Rev limiter may or may not kick in, but who cares if you blow your motor at that point? At least you'll be able to stop and steer.