The general opinion is, that it is fine when the result is between 8-12.
It is overrated and I don't give much for it. Today you have different materials in the Arms (Steel, Aluminum, Wood, Titan etc. etc.). There are also different Tonearm geometries out there, some have less distortions at the beginning, some more in the inner grooves, most audiophiles think, when they buy an "Arm" then it is done perfect in every way but I think, that's the mistake of their audiophile life. Did no one ask why some arms are straight and some not? And why? (the straight ones are cheeper to make and need no knowledge...) and what the arch angle is good for? .....
These materials all have different resonances. Next, you have different kind of bearings (from construction and from design). these differences can be huge.Or, is the Arm a rigid design or not, what's with the energy transfer?
How fast is this one? Does it even exist, or does the Arm save it to a momentum and starts to vibrate on its own and reflects this back into the tracking process...long story short: does it allow fast transient transmission?
Back to life
I have (and had) combinations which have been between 9.7 -10.0- 10.4
Nearly super (from that Theory) but I was amazed that some carts performed MUCH better in Arms where the "calculation" showed different datas.
This calculation is more or less a help but after all I don't give a dime for it. A good designed tonearm is much more important.
I wrote several times about that when I made my comparisons with my Arms and Datas and the result was always the same, the best quality Arms worked best with a lot of cartridges at superior level.
And other Arms only with a few ones.
Btw. Cartridge Design does not stop with compliance. Their reaction with a tonearm can be totally different, but you will never read something about that. The best cartridge is a sold cartridge and based on that you will also find the general "recommendation" about loading: 100 Ω 47kΩ :-)
Example: Lyra Titan / Olympos are superior from sonics in top Arms only (energy transfer via Headshell into the Arm), when used in Arms with cheap bearings or bad geometry you get an analytical sound which is not a pleasure to listen to.
But let's not forget: All has to go through a Phonostage and that one can change the results also. Or, even more audible, internal turntable vibrations (Bearing, Belt, Motor(s), Platter, Suspension ...), in my personal opinion, I think, they degrade the possible maximum from sonics more than anything else.