Meantones of 768

As Graham pointed out, it's not really necessary to use the same fifth
to get a decent meantone. However, it might be worth looking at the
available meantone fifths for the 768-et

149/256

This is a good Mozart-type meantone, .07 cents flatter than 39/67. It
is interesting to note that this meantone is also available in 512-et
systems such as Paul's.

223/384

This is quite close to 18/31, with a fifth about a tenth of a cent
sharper.

445/768

This is another good meantone, .32 cents flatter than Wilson and
.58 cents sharper than 19-equal.