Graham, isn't the vertical compliance around 4-5cu?
That's extremely low and will certainly drive an arm hard.
They have much higher lateral compliance which is around 20-25cu IIRC.
Makes finding the ideal arm difficult, and likely why damping is recommended since it will lessen the effects of any mismatch - and there will be one with any conventional arm. Unipivots of course usually have damping so no surprise they've been favoured.
Decca quote the following Rob:
FFSS head
Lateral 15 x 10 (-6) cm/dyne
Vertical 4 x 10 (-6) cm/dyne
Decca Super Gold
Lateral 12 x 10 (-6) cm/dyne
Vertical 5 x 10 (-6) cm/dyne
Decca London
Lateral 15 x 10 (-6) cm/dyne
Vertical 7.5 x 10 (-6) cm/dyne