When Klemeperer recorded the Missa Solemnis, EMI hired the Wigmore Hall (I think it was at least) to promote the recording by playing excerpts and having the producer and engineer talk about it - Decca did much the same with a series of their spectacular recordings in the 60's (Faust, Mahler 2 with Solti - first dolby processed master tape - and Gotterdammerung for example).
The Klemeperer recording was treated as a major musical event and so it proved. It left a great impression on me, in particular, the Gloria has a power unequalled by any other performance I have heard, aided to a tremendous extent by the utterly extraordinary Philharmonia Chorus who were prepared for the recording by Wilhelm Pitz. There are several other stunning performance on record from this choir at this period, truly a golden age for their work.
Of course there are other fine recorded performances of the Mass but for me nothing equals the Klemperer. I wonder if anyone else feels the same?
Personally I think nothing can match the effect of period instruments, but that aside there is one thing I can say about these old recordings, or rather their CD incarnation - if you can't fit the recording on to one CD then it should go in the bin, because there must be some serious tempo issues going on if you can't. I've had a few old recordings that fail this test!
