Open Stack

I'd like to get input from the community on a 'realistic' size of a small Swift cluster that might be deployed & used in the field for production. SAIO / test / lab setups aren't a consideration. I'm interested in hearing about both private and public cluster sizes that are deployed for actual.
 4 nodes or fewer doesn't  seems pretty small - 6 or 8 seems like a more realistic size of a small cluster. But I don't have any actual data/customer experience for those assumptions.
Followup questions:
Given that cluster size,  do all nodes act as both Swift proxy and storage nodes? I assume they do.
How big does a cluster get before node roles are separated?
Thanks for the input,
Tim
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