How important is low W & F performance anyway?

Why asking for that goal?  along the title of your thread and what you posted in your answer to my question makes me to think why are you asking those questions?

Because having spent a great deal of time and effort to achieve that goal seems to be all for naught if tables that measure much worse are perceived as desirable and receive universal praise; it makes me wonder if we were chasing the wrong goal.  I likened it to the specification wars of the late 70’s and 80’s for ultra low distortion figures in amplifiers that turned out to be a false beacon in the night.

Apparently engineers and audiophiles think very differently about things.

Fascinating topic 

I have a venerable idler-wheel Garrard 301 and a new belt-drive Holbo air-bearing system.  I don’t have pitch perfect hearing and I’ve never noticed wow or flutter on either of these decks.

The Garrard's speed increases very slightly from cold over about 10 minutes before attaining its stable speed - something noted in the original manual for pitch sensitive applications. Garrard specifies wow and flutter separately - wow less than 0.2% and flutter less than 0.05%.  Furthermore, Garrard specifies exactly how these have been measured - using a Gaumont-Kalce Wow and Flutter meter Type 564 with 3000 cycle constant frequency records at 33.3, 45 and 78 rpm.  Very much an analogue device, one of these meters popped up for sale recently for $400, but how would you know if the meter itself is correctly calibrated?

Each Garrard was delivered with individual hand-written test results for wow and flutter at each of the three speeds - six numbers in all.

On the other hand, the Holbo does not seem to include wow and flutter in its specifications at all.  With a 5-kg platter and an air bearing, it is pretty free-running.  If the belt is removed, it takes about three minutes to come to a stop from 33 rpm.

A review of the Holbo Holbo Mk2 Airbearing Turntable System | Tracking Angle includes so many speed stability measurements that my head is also spinning - from 0,116% peak W&F to 0.016% WRMS (weighted root mean squared).

Here is the nub: what weighting curve is used?  It varies depending on the particular standard you choose.  Most of the European-centric standards seem about the same, but the Japanese are quite different.  Couple this with the wide variety of averaging methods - peak, standard deviation, two standard deviations, root mean square, average and simple numbers could mean almost anything.

From what I’ve read, wow and flutter is most likely to become apparent on solo piano recordings.  A reverberant listening space might allow the decay from a note to interfere (beat) with a reflection of the same note emanating at a slightly different speed.  I’ve never noticed this, but have not been listening for it either. 

Ability to achieve such low numbers (if true) gives us a feeling the maker has the ability of precision manufacturing, i.e. nearly friction free tonearm , quality decisions regarding din connectors and cables .... 

Measure meaningful metrics and listen…

the ear / brain is the hard part

there is also

bright shiny heavy hardware attraction ( fishing lure effect ) …

@elliottbnewcombjr 

Ability to achieve such low numbers (if true) gives us a feeling the maker has the ability of precision manufacturing, i.e. nearly friction free tonearm , quality decisions regarding din connectors and cables

Not sure if you are commenting in general, but if your comments are directed at the Holbo I think they are pretty accurate.

The tangential tonearm rides on a 10-micron layer of air and seems totally friction free. It is connected to the deck by 4 Litz wires and a very fine air tube. These hang from the arm before looping up to the deck - there is a long slot in the deck for clearance.

With the arm set at zero tracking force, there is no friction between it and the raising device.  An adjustment screw allows the arm bearing rod to be levelled horizontally, and the arm responds immediately to tiny adjustments.  It tends to centre because of the very slight pull of the Litz wires and air tube.

The Garrard was made well before Computer Numerically Controlled (CNC) machining was even dreamt of.  It has no feedback mechanism to govern speed, but it is continuously braked by an adjustable eddy current brake operating magnetically on a aluminium disk rotating at about 1000-rpm on the motor shaft. A big knob at the front of the deck controls the position of the magnet and therefore the amount of braking effect, and provides fine adjustment of the average speed. This is easily seen under incandescent lighting  on the strobe patterns cast into the rim of the platter - a two Pound Sterling option when the table was new.

The motor has four shaded poles, so it is not quite synchronous, instead slipping slightly with the braking effect and stylus drag.  Personally I think stylus drag is tiny compared to the eddy current brake, which could explain why these decks are valued for their 'drive' when playing heavily modulated passages.

I don't think the Holbo has any feedback mechanism to fine control its speed, either.  Unlike the Garrard, it is not designed for end-users to disassemble . There are separate trim pots for 33 and 45-rpm, but they need a small screwdriver and are round the back and fiddly.  Definitely a set-once and forget proposition.

The round-section 'belt' is far smaller than I expected and stretchier. Nevertheless it gets the 5-kg platter to speed in about 4 seconds while providing good isolation between the platter and the motor.