Well.....
I'm pretty honest on these things. Don't try to sell you something you don't need.
You know, it really depends on what you want to do with this boat. Do you plan to actually stand up and fish? Depending on the river, high flows are still no big deal (I STRESS depending on the river). If you only plan to float and fish from shore, get the watermaster. You won't need the super expensive one. Just a vehicle from point A to B. But if you want to anchor up, or get up and fish while you're floating a stretch. Then get the Steelheader by Skookum. I've spent many days, especially during the summer, floating stretches of water. I usually free drift and stand up and cast to slots coming up. Plus, if you have a fish on it's easier to play around the boat then being stuck in the seat. You can quickly drop anchor and play out the fish to the boat.
So, if you want what I described above fishingwise, get a Steelheader. But, if you only plan to navigate to next spot, then go with the watermaster. You don't need anything hardcore on most of these rivers, unless you plan to fish really high water (which is normally a conventional fishermen's domain anyways). Plus, most decent fly water is within the realms of most class II's, maybe the occasional class III. I like to hit the UPPER stretches of rivers, normally class III/IV isn't unheard of up in the headwaters. Good luck, just make sure you decide exactly what you want out of a boat before you buy. Easier to by the right one the first time, then have to sell and rebuy. Get's costly that way.