variance of +/- 10 Hz with 1 kHz test tone

That level will make a difference in clarity, decay, imaging, even if you notice no obvious speed instability.

I've seen a lot worse on a lot more expensive turntables, brand new. That does not make it right.....or good......but it's not unusual.

Should I try another platter to see if my current factory Rega one is defective?

If I'm not mistaken that level of performance translates to .02% away from what a casual internet search showed to the best to be, a VPI TT with .01%

Anything that bests .1% exceeds NAB specifieations.

"Wow and Flutter Factor (Re~ording)~
1.15 It shall be standard that the average deviation (measured over the range 0.5-200 cps)
from the mean speed of the recording turntable, when making the recording, shall not exceed
0.04% of the mean speed. The average deviation above shall be measured by a meter the dynamics
of which shall be the same as those of the VU meter as specified in ASA Standard C16.5-
1961.
Wow and Flutter Factor (Repr~ducing)~
1.20 It shall be standard that the average deviation from the mean speed of the reproducing
turntable when reproducing shall not exceed 0.1% of the mean speed."

I can't remember anything that would suggest the NAB would want to drive listeners away from either Am, FM radio because they were sloppy or uncaring with audio performance.

Because today, many turntables routinely perform in the range of .03% or less can't possibly mean your head might spin when listening or that performace in the .03% to .01% isn't top notch.

That's about 0.1% isn't it? maybe sounds a little on the high side...

@Gvasale and @Atmasphere, what is the formula you are using for these calculations?