Ya it wouldnt take long for the sm to get put in its place. I know they seem aggressive but wait until you see a pairs of red devils, green terrors, convicts etc. They make it seem like a neon tetra lol
Pbass aren't known for their aggresion, unlike the other cichlids you listed. The same is true for smallmouths, as sunfish go they are not known for their aggresion. The combination might work but what concerns me most is the temp. A smallmouth would do much better long term in a cool water tank (60's maybe low 70's) and of course the pbass is tropical. As for size, some pbass are smaller then others, it would depend on the species.