I was thinking of ordering about 6-7 1" Vieja and was wondering if I could possibly keep them with a 4-6" Pearsei? Everything I've read is that they are gentile leaf eaters so would they not pick on the smaller fish?
Even peaceful fish are opportunistic. I would not suggest keeping the two groups together with a Pearsei that much larger. While they are not considered aggressive, they get extremely large, very quicky. Think of their temperament like a very robust severum. I think if the vieja were a bit larger 2-3" or the Pearsei were a bit smaller 3-4", you would probably be fine... again depending on the size of the tank and other occupants.
I think you would be better off if the fish were 2" and the Pearsei were 3-4". Again it would also depend on the type of vieja/paratheraps you end up going with. Some are much more aggressive than others.