One thing that works against drivers in an unintended acceleration situation, is when they first panic and press the brake, although it may overpower the engine, it won't be a screeching halt, so they may release the brake and reapply. If the engine is at WOT, there will be no vacuum, and the vacuum reserve for the power brakes will be depleted, and the brakes will require a substantial amount more effort.
Try this exercise: Stop a car at the top of a hill (steeper the better), put it in Neutral, and shut off the engine*. Release the brake, now pump it several times to deplete the reserve. See how much force you need to slow the car down. In my experience I basically need to prop myself up with my shoulders, and put all my weight on the pedal. That's as an able body male in a compact car coasting down a hill, not as a frail old biddy mashing the brake and gas in her Camry.
*Someone's going to complain that shutting the engine off will lock the steering. In every automatic I've seen, if the shifter isn't in park, you can't turn the key back far enough to lock the steering, only shut the engine off. With manuals you usually require an extra release button, or other noticeable detent to move it back to lock. You only need to move it one detent. Hell after you kill the engine you can move it back to ON, as long as the engine isn't running. There will be a loss of power steering, but it should still be controllable especially once rolling. Automatics usually only allow a restart in Park or Netural, by using Neutral if you can't overcome the brakes, or steering, restart the engine (will not work in DRIVE, REVERSE, or LOW). In a standard you may want to try leaving it in 2nd, with the engine off but ignition "ON". That way if you need power you can pop the clutch, or restart with key.
The first reaction in the case of a runaway car should be to shift to neutral or de-clutch. All modern cars should have a rev limiter to keep from exceeding the redline, and many modern automatics (at least, don't know about manual) have a very low revlimiter if in neutal or park (they will only go up to 3-4000RPM when the engine redline is 6500RPM), so engine damage shouldn't be a concern. Second reaction if that doesn't work is to shut off the ignition (I hate push button ignitions for this, you usually have to push and hold for a couple seconds for a forced power off... Just when I thought an ATX powersupply was a PITA with a crashed computer) . Third should be to try any available parking brake (don't know how the stupid new electric parking brakes would work), and finally as a last ditch effort, I'd try Park as I look for a nice guard rail I could graze against.