Were they that good?Yes, in many cases.
I have many of the Sheffield Labs d-to-d releases, both popular and classical, and one of the M&K Realtime releases (the organ recording "The Power and the Glory," which is spectacular).
Some of the Sheffield classical releases were mic'd a bit too closely, resulting in an overly bright string sound, and somewhat dry acoustics. But in all other ways they were very special.
Many of the Sheffield's have been re-released on cd. I own two of the cd re-releases, and in both cases I also own the original d-to-d vinyl releases.
I was reasonably pleased with the cd version of Volume I of "The Sheffield/Leinsdorf Sessions," containing Prokofiev's "Romeo and Juliet," Debussy's "Afternoon of a Faun," and Wagner's "Forest Murmers." I would not recommend it, though, to anyone with a system that tends towards excessive brightness, for the reason I mentioned above.
I was very displeased with the cd re-release of "The Sheffield Track and Drum Record." The original d-to-d release of "The Sheffield Track Record" had been proclaimed by Harry Pearson, at the time of its release in 1982, to be "absolutely the best sounding rock and roll record ever made." The cd re-release, however, I found to sound dull, dark, closed in, and completely lacking the magic of the original vinyl release. I was not particularly astonished to subsequently read in the liner notes that the cd was mastered by "playing back the analog disk with a Technics SP-15 turntable and a Shure V15 Type V assembly attached to a SME 3012R arm."
Best regards,
-- Al