Reducing the log of the keyspace by 4.16%, which is not a particularly interesting measurement.

Reducing a key by 8 bits reduces the key space by 255/256, regardless of key size.

I don't see how that can be, given that the character that's chopped off can take one of 40 values... Or is it case sensitive? Still, nowhere near 256.

It's not b64 encoding the final byte of the hash, not dropping a b64 character.

Ah, I see. You are correct, then. Also, that would make it 64 times, if I were right, it seems.