My guess is 5-6 feet. But I'm in Utah and have no direct knowledge of Idaho conditions. I take the MS flow at Shoup and add it to the MF flow at the mouth/Shoup to get a ballpark. I generally go by the guidelines in the Eric Newell guidebook, with 2-3 feet being moderate, 4-6 feet being high, and 7+ being extreme. I'm a very conservative rafter, so around 3-3.5 is my comfortable maximum. Yes.....I'm a wuss.
"We are all visitors to this time, this place. We are just passing through. Our purpose here is to observe, to learn, to grow, to love....and then we return home."
Australian Aboriginal Proverb