a raft moving upstream....
I don’t know what your expectations are exactly, but I think you need to lower them. J/k. But I think you’re right to be a little nervous about how well this might work.
I haven’t been on the rivers you referenced. I have spent a lot of time fishing on slower sections of the upper Snake River in Idaho. From a row boat. Eventually a drift boat. Most recently a John boat. I also row a raft, but learned the raft after years of the other boats. (You might be able to identify me and my buddies move up into higher wages by that list of boats 😉
I can only share my perception and experience. Hope you find it helpful.
A two stroke 6 hp (I think) evinrude (yeah from back in the day-we were both young and broke and this was mid 1990s) would barely move us up stream in the row boat. I don’t know current speed (and that river is constantly speeding up and slowing down anyway as it goes deep/shallow/wide/braided channel etc) but, I can offer this (probably useless) comparison. We could never really row upstream because the current was too strong. We could hold position rowing, but not really gain. And totally spent physically after less than a minute trying. The drift boat made holding position in strategic locations much more possible.
....pause for effect.....
This what I mean when I say it would barely move us: It did move us upstream in the row boat. And we noticed that weight distribution was way more important than actual weight. We would go up stream, at full throttle, for what felt like a full minute or so to retrieve an expensive lure or a favorite fly that snagged up. A full minute-ish to go only as far as the amount of line on our reel...or less.
A row boat. A 6ish hp motor. Row boats are pretty efficient on the water. Rafts are horribly inefficient on the water by comparison. When I learned to row a raft I was shocked at how much effort was needed to move an empty rig. And moving it fast has never happened in my perspective. Additionally, and this is important, a row boat is very ridged and has a keel, so it responds to current and motor and weight distribution- all of which add up to an ability to steer when going up stream. My fear (although I don’t know) is that the current will simply push the nose of the raft a little left or right and you won’t be able to get it straightened out before the current finishes pushing the nose around so you’re pointed down stream again.
Just my opinion, but you better test drive this rig before committing the high $$. My guess is that you might hold your position in the current and possibly, just maybe, go upstream at the same speed you could have walked upstream after you rowed to the bank. Even if the bank is a tangle of brush and branches. Walking might be more enjoyable too; stretch your legs and not listen to an engine scream for several minutes.
A fair number of guys do fish out of a raft on the river, I’ve just never seen any of them so much as attempt upstream travel.
Of course current speed and current uniformity (ie eddys or confused water verses water flowing in a uniform fashion) will make a huge difference. You know your river; my experience might not be similar to yours.
Good luck on the decision! And post results. I’m curious now.