It would have to be an absolute freak of a fish. A 4 pounder is a rare fish and I've yet to even see a 5 pounder since I started fishing the rivers a lot and doing tournaments in 2012. I've never heard of anybody catching a legit 6 pounder from any of the central MO rivers, but I'm sure it has happened at some point over the years. The two most impressive river smallies that I now of both came from the Gascoade. My buddy Tommy caught one back in 07 or 08 that was 23"+ and weighed like 5-11 or something in that area. @Mitch f's buddy caught one that looks like an absolute freak in the picture. I don't think they got any measurements on it though, but it looks like the closest thing I have seen to a 6 poung river smallmouth that I've ever seen. The river smallies just don't have the mass that lake smallmouth seem to get.