Forms of verbal address between officers and soldiers.

[Maiorianus]

Gabriel, I disagree slightly with your point No. 3: Modern British practice does not reflect (indeed may be a reaction to) historical behavior. The British Army has been around a long time, and the way officers, non-coms, and enlisted men behaved toward one another has changed drastically over time.

Which actually supports your idea that the behavior of the Romans over time probably changed, as well.

You're absolutely right. I just wanted to underline that, even where class differences are important, they are not always prominently displayed in public behaviour, because some societies privilege other values (understatement, restraint, etc.) which act as a counterbalance. Roman republican society, with its stress on exactly those values, would seem to me one where use of seniority/rank titles would have been quite limited. The Empire, again, is a different story....