I've seen them get up to about 2 inches, but ya not quite that big. They are very pretty at that size though.
But I would say with these, likely if you get them healthy and happy they will color up better and it will be easier to tell which kind they are. When I got my gbta, it was in a fairly stressed state. It was bright purple with long narrow tentacles for several months and slowly regained it green, and is now bright green with purple tips and big fat bubbles. I knew it was gbta from the start but if I hadnt it would have taken several months before it would have become clear as to what type of nem it was.