+1 on a texas... I had to rehome a 4" male because he was kicking the crap out of everything in the tank (a 180 gal, all other fish were at least twice his size).
Although a 75 would probably be best for a texas, they are fast and very active. A 55 would give you plenty of time if you bought a younger specimen.
I also read a thread recently where someone mentioned exodons... I've been somewhat preoccupied with wanting a shoal ever since lol. You could probably fit a small shoal in a 55, I think a lot of people get away with 40 breeders (although that feels a bit extreme).