Shap -- diggin the new avatar!
Take this with the usual grain of salt BUT:
I have rowed a 14' bucket boat down the Bruneau at 500. I've also rowed a 12.5 cat on the MF at 1.7 feet.
Obviously those are very different boats. HOWEVER -- in my opinion, the Bruneau at 500 is a solid class harder than anything on the MF at those flows.
The move at Ram's Horn is more consequential than anything I noticed on the MF. Devil's garden is much long and tighter than anything on the MF.
I would agree with folks who say the MF is III at low water. The bruneau's Five Mile section is class IV -- solid class IV -- at ever flow I've seen. And I've been there at 450, 550, 700, 1200, and a few more 500-700 cfs laps.
I dunno what to reccomend in Idaho, but here in Washington, the Green River Gorge at 1000 cfs is the best approximation of what I experienced at 1.7' on the MF.
But man whatever you do DO NOT put a novice on the sticks in a gear boat for a low water five mile run on the bruneau.