should the ZS172FMM-6 be 6 speeds?

[ProDigit]

Depends on the intake and exhaust. Is it a freeflow system, or the more restrictive stock system?

A free flow system can idle at lower speeds than a restrictive system.

I guess in some way (outside of the obvious ambient or engine temperatures), the oil thickness also plays a role, but I see no reason not to idle at 1k rpm, so long the idle is consistent (and not constantly oscillating between 800 to 1400 or so).
So long the bike doesn't stall...