[ricard]

I think that in practice at least machines using the same type of spools would have used the same speed - heads and amplifier designs would have come out of a common source, and few manufacturers would bother optimizing their designs by using different wire speeds.

Using computer software such as Audacity can help you adjust the speed (pitch) of recordings. Granted, it's not the same experience as actually listening to the spools on the machine but can be immensely helpful for sorting out recordings made at the wrong speed.