Quote Originally Posted by Quirinus
While we're at it, does unit size affect the duration/speed of battles? For example, if I pit two units of hastati together, does the fight last longer if I set the unit size to 160 men than if I set it to 40 men? Or do individual men in large unit sizes just die faster?
Yes, they do die faster - battles are of even speed on huge unit size as to small unit size since proportions/ratios are maintained.

There is one slight change in battles relating to charges - especially ones involving cavalry. On smaller unit sizes, the units which are being charged into are not as adept at absorbing them. This is due to their lines being overall thinner. Due to this, the charges generally take out a slightly higher percentage of the unit.