Previously I had a site that had a fully loaded norstar MICS 4.1XC. Every digital port had a phone, every fibre port had station modules, 2 - T1 cards, and a fully max'ed out companion.
The system ran fine, 8 port nam was flawless, only slowness we saw was on things like the caller ID inbound was not instantaneous on the display, it took half a second. Some other functions took half a second to update as well, although it wasnt something that the user complained about. We upgraded them to a 3 cabinet Option11c with call pilot.
I'm writing because i'm not sure if this idea is feasable - i've never tried it, but know a tech with a site that does this over analog trunks.
He's got many sites all norstar 6.1 mics, nam with multi-level ccr trees. When customers call his sites, the AA/ccr tree answers, gives the callers options then transfers them using routing codes - which flow out on analog trunks to other sites. I'm wondering if you could set up the 2 norstars next to each other, either E&M analog or T1 cards between each other (since 6.1 can do more than 2 T1 trunk cards now - in a trunk expansion module), set up the T1 cards to be E&M trunks between the switches, and use routing to send calls between the 2 ksu's?
Set up the 2 KSU's to have different extension number ranges, then use routing codes between them that match the other ksu's extension numbers for user transparency. then you wouldnt have to load one up to the max... I dont know all there is to know about 6.1 yet, so no doubt there's a better way, its a thought.