The flurry of responses has started to wind down. They are all well thought out and great. Thanks.
So here's an update to my suggestion:
The major 'flaw' in my suggestion is that if you model specific consists you will end up with ops that are 'boring' (over time) ... unless you have a fleet that is much larger than the normal layout. I agree with this.
So what if your -fleet- is modeled based on actual train consists ... but you don't use those consists for your ops - or if you do use them duirng ops you only do so on a few trains or only on "special occasions"? - Jim