Cylinder pressure is indeed the big deal.
The camshaft specs - and obviously ignition timing - will have a fair amount of "input" on octane requirement.
Also, the load the engine's under in whatever the operating scenario is.
Details like no sharp edges in the chamber matter as well.
For something like a 3500-lb car. 3.55-4.10 gear, street 440, alum heads, 220-240 @ .050, on 93, I've run 10.0/10.3 static (measured).
None rattled/pinged, all had great response, but that was pretty much the max CR on 93 for me.
I do have a policy of never lugging a performance engine.