TT speed

 I am still thinking tracking error, but the aspect of speed throws me off that idea. 

At least it is not a large number, but maybe it accounts for a tiny perception of tonality in people with pitch perfect hearing?
(Not me)

Any alignment of a radial arm is a compromise. The alignment procedure is supposed to achieve the least amount of distortion across the entire record surface, not eliminate distortion. So, to fuss over it excessively is futile.

Use an arc protractor.

Align stylus tip to arc for full sweep. Make parallel to only 1 grid, inside or outside, your choice. DONE. No guessing. No trial and error, no back and forth. The 2-point protractor is archaic and very inaccurate. 
 

I have 123 cartridges, so doing alignments is common. Takes about 5 minutes. I use Lofgren B DIN mostly. Sometimes Stevenson DIN. The Arc protractor is deadly accurate and quick. I use it for conical, elliptical, HE, LC, MR tips. I get no IGD. Haven’t heard that in years. 
 

For printing your free arc protractor, you need your pivot to spindle distance; it’s a spec for your turntable or you can measure it. Choose your alignment (Lofgren A/Baerwald, Stevenson, Lofgren B) EIC/DIN/RIAA null points, and print. Easy peasy!

You are connecting two parameters that are not related. The stylus tip does not need to know where it is on the surface of the LP in order to reproduce the frequency accurately. It’s essentially a point in space.

For any pivoted tonearm, the stylus will describe an arc starting at the outermost grooves and swerving inward to the right of the spindle as it heads toward the lead-out grooves.  When you use a typical 2-point protractor, like the Feickert, you can see this effect, because the protractor is helping you to locate the stylus and cantilever at each of the two null points defined by any of the 3 standard alignment algorithms.  By definition, the stylus tip and cantilever should be parallel to the groove or perpendicular to the center of the spindle, at a null point.  You have to rotate the protractor to set each of the two null points because the tonearm pivot defines one and only one arc upon which the null points have to be set.  Please try to visualize that if my words are insufficient.  Alignment can affect distortion characteristics, but it does NOT affect fundamental frequency.  Because no matter where you are on the arc, the cartridge is reproducing what is encoded in the grooves at that point.  When a test LP with a 1000Hz tone is created, it is done with a lathe that ideally automatically compensates for the changes in groove length (a spiral with an ever diminishing radius, heading toward the lead-out grooves).  Your rotating the protractor is just to locate each of the two null points, has nothing at all to do with speed accuracy.  So long as the platter maintains constant speed, 1000Hz is 1000Hz everywhere on the LP surface.