I saw a post on here about 6 and 8# smallmouth from the Umqua. I can't say it never happened but I doubt it. I'm now too old and lame to make the drift but until a few years ago I did it regularly from Scottsburg to the sound. I've seen 5# fish from the Umqua but they are rare indeed. What is true is that if you don't land 200 fish you've had a bad day. Most of those fish are less than 2#.
That drift, by the way, is about 10 miles as the crow flies and there are a couple of short portages. At the rate you catch fish, it takes 2 days to make the drift. Banks are almost solid blackberries and brush. Places to camp are nearly nonexistant. Start looking early. Your best bet is to find a sand bar.