Hey, I've just thought of summat... 
Andr'e, you used an FR64S and found CD vastly better! HiFi Dave used an SPU - IN AN FR64S and found the combo wanting..
I'm wondering if the FR64S is just not cutting it in terms of sound quality. Forget the cachet of such an arm for a minute, I'm talking of an arm which actually may not be as good as 1970's golden memories of it are....
P.S. My favourite 301/401 combinations were with SME's with properly matched cartridges, the Transcriptors "Fluid Arm" with ADC XLM and a couple in Bastin plinths with NAS tonearms (the old Omega Point arm/Decca was an awsome combination with a Garrard).
I'd agree with Andr'e about mains voltage affecting 401 motor speed and before too long I'll locate the early 70's article and scan it to post here as proof. The 401 didn't use a beefed up "Synchro Lab" motor, just a heavy-duty induction type as I recall and these are sensitive to mains voltage changes.
I can't go on and I can't go back, I don't feel so matter of fact,
I tried and tried to make good sense, What's the good to try it all again?