The attackers won 463 times.
The defenders kept the stronghold 537 times,
including 32 mutual destructions. The battles took an average of 2.9 rounds.
Presses left before reducing an Elite controls how
you take casualties. For example, if you have 2 regulars and 3 elites and need
to take a casualty, should
you reduce an elite or lose a regular? If you lose a regular, you're only
rolling 4 dice, but you could potentially have an extra press.
Say you have 4 elites in your army, so you have 4 presses left. If "Presses left before reducing an elite" is set to 4 or lower, you'll reduce an elite when you need to take a casualty (and then you'll have only 3 presses left). If the value is set to 5 or higher, you'll lose a regular (reducing your combat strength below 5).
Of course, if you have more than 5 combat strength (including Captains of the West), the simulation will always take regulars as casualties first.
The attacker always fights until the defender is destroyed or there's no way to press any more.