I'd suggest either changing this thread's title (if possible) to "How do I change the system's model identifier?" ---if possible, I've never tried it on this forum---or begin a new thread, since that's what you want to know, not about speed step, am I right?
In my experience, unless you target your thread titles perfectly with someone else's experiences it'll get overlooked here.
Sorry I can't help your issue however. The newer NBI you ran---was it NBI 2000 blah blah (long name, specific to the later versions of 10.6.)?