Having recently finished a Gaulish campaign, the following ideas occured to me.

Towns that have buildings that give combat bonuses (e.g. the Blacksmith series, or the Temples to Toutatis) may be better off making larger-volume units (e.g. Warbands and similar infantry). For example, a large temple of Toutatis will then add 3 x 60 = 180 chevrons to a 60-man unit, as opposed to 3 x 27 = 81 chevrons to a 27-man cavalry unit (on medium-size unit settings). This of course translates to proportionately more attack and defence power (and morale?) to the larger units.

On a similar but unrelated matter: the 'best' unit size setting to play on may depend on which faction you're playing. The larger the unit size, the more you deplete your settlement population to recruit them, and hence the slower your settlements grow. For very 'civilised' factions that depend on high-population cities to reach the top of their tech trees (e.g. Romans), a small unit size is advantageous to allow faster population growth. For 'barbarian' factions, whose cities top out at 12000, larger unit sizes and slower population growth are an advantage, and a handicap to their more civilised enemies.

Anyway, just thought I'd mention it.......