There is no need to use loq qualtiy Vocalizer voices on a 64mb device.
With the 9.400 NC and the good old Kate I have over 20mb free ram which is more than enough for me.
12mb is a bit low, but that is not caused by the voices - it is the Navcore and/or emulation.
The 9.004 on my 730 is over 20mb too and offers "truck features" for normal maps.
The 9.400 offers instructions through FM.
So before you mess with the voices I suggest to try some different NC's