Well, now, we have better understanding of the traffic simulator and its properties, and so far I say sim Z is the best. I am a member of the NAM Team (Got on last month or so) and pretty much now, sims are commuting more realisticly. However, we have found that the "better pathfinding", "perfect pathfinding", and "2,5,10x Capacity" sims are actually not good for the main simulator.
Vince
EDIT: Also, due to EA's EULA, we can't edit the Source Code and distribute it, sadly.