Pick one and press Start, then click Next › to step through it.
The headroom sitting comfortably above one, and the crossover landing exactly at the single-node ceiling.
That scale is the trigger for the fork: a relational primary buys joins and transactions until the write load outgrows one node and forces you to shard.
Size the write load against a single primary's ceiling, count the shards a scale-out would need, then drag the write rate past the ceiling to watch the answer flip.