City Comparison by Race

[Anthony]

If you march out spearmen of High Elves, High Men, Nomads, or Orcs, even before a marketplace, with heroism, they can take most cities.

My experience is that I'd need multiple elite units unless I'm talking power races (barbarian, halfling, gnoll, lizardman), which is a fairly substantial mana investment since some will have to be cast overland. But yes, it's doable if you're playing with life books.

[Incanur]

Skeletons can also be effective summons very early on, especially with 10 Death books and Conjurer.

[Catwalk]

Raising taxes to 2 and building extra spearmen is almost always a good deal. Depends on how expensive they are, but even with trolls I'd do it as those spearmen become elite eventually just for boosting your economy.

[Anthony]

At base production, gold, and food rates, a city has the following per unit population:
Tax rate 1.0: 0.5 farmer, 0.3 worker, 0.8 gold, 0.85 production
Tax rate 1.5: 0.5 farmer, 0.2 worker, 1.05 gold, 0.65 production (+0.25/-0.2)
Tax rate 2.0: 0.5 farmer, 0.05 worker, 1.10 gold, 0.35 production (+0.05/-0.3)

Given that 0.3 production can be turned into 0.15 gold, that obviously favors rate 1.5. Now, if instead we start adding spearmen to negate unrest, we have:
Tax rate 1.0: 0.7 farmer, 0.3 worker, 0.4 spearman, 1.0 gold, 0.95p
Tax rate 1.5: 0.8 farmer, 0.2 worker, 0.6 spearmen, 1.5 gold, 0.8p (+0.5/-0.15)
Tax rate 2.0: 0.95 farmer, 0.05 worker, 0.9 spearmen, 2.0 gold, 0.575p (+0.5/-0.225)

If we rate production and gold as equal value, for cost 10 spearmen we have:
1.0->1.5: +2 production cost per citizen; net gain +0.35 per citizen, ROI 17.5%
1.5->2.0: +3 production cost per citizen; net gain +0.275 per citizen, ROI 9.17%.

That's not terrible, but it's mediocre. Still, might be worth considering.