When it comes to fish eating other fish, I can safely say my Leiarius pictus has eaten fish as big as itself. When he was about 4" he actually ate a 3-1/2" Acestrorhynchus falcatus. Speaking in terms of relative size, this was the most incredible things I had ever seen. That catfish has eaten more fish than any of my cichlids.
And as far as bass go, I know largemouth will go for anything up to about 50% their own size.