This morning without putting a whole lot of effort into this, I was able to winnow it down to 27.32 bits per word without any other trickery like 5bit packing. You need at most 1 bit per word to identify the real words, so that's 27.32+1 bits without the bitpacking. Doing 6 bits per letter drops that by 25%.
Now having put too much effort in, I'm around 21.6 + 1 bits per word, (17 bit packed) just by using SSP.
This morning without putting a whole lot of effort into this, I was able to winnow it down to 27.32 bits per word without any other trickery like 5bit packing. You need at most 1 bit per word to identify the real words, so that's 27.32+1 bits without the bitpacking. Doing 6 bits per letter drops that by 25%.
Now having put too much effort in, I'm around 21.6 + 1 bits per word, (17 bit packed) just by using SSP.