DrwHem: First Cohorts do have a slightly higher attack, defense, and morale. Unfortunately the increased size makes them masively unbalanced compared to other units, and also makes it possible to stuff 50%+ more killing power into one stack. I think the Romans already have it pretty easy after the Marius reforms without that.
Still, if you want to make the change for your own game, then it is pretty easy to do. Just open up [rome]/xgm/data/export_descr_units.txt with notepad and change the first number on the solder line of the "roman legionary first cohort ii" entry from 40 to 60. It should look like this:
Code:
type roman legionary first cohort ii
dictionary roman_legionary_first_cohort_ii ; Legionary First Cohort
category infantry
class heavy
voice_type Medium_1
soldier roman_legionary_cohort_ii, 60, 0, 2.2
How random are these crashes? Does the same battle work if you just reload your game and try again? If so then it's probably a memory or graphics issue. You are playing on huge unit settings, which can put a strain on many machines, and RTW has a memory leak problem which will make the strain worse the longer you play.