Here are the speeds on the strobe discs that accompany Aida  
Favia-Artsay's Caruso on Records.

50 Hz:

68.18
71.43
73.17
75.00
76.92
77.92
80.00
86.95
88.23


60 Hz:

67.92
71.29
73.47
75.00
76.60
78.26
80.00
86.75
87.80

There is also a good discussion of this in Michael Henstock's Fernando  
de Lucia, Son of Naples (which also happens to be the best example of  
musicological research I've ever seen).

HTH.

Howard Sanner
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