Let's note that this fall apart in Metropolitan French, where we don't say neither « septante » for 70, nor « nonante » for 90 (and even less « huitante » for 80), but « soixante-dix » for 70, « quatre-vingt » for 80 and « quatre-vingt-dix » for 90.
It's quite a shame, because that solution for reading hexadecimal numbers out loud is quite elegant :)
I personally prefer octante. Septante and huitante sounds to much like just slapping -tante to 7 and 8. And just to be coherent, I would love to have heptante for 70.
"septante", "octante", "nonante" would be coherently based on Latin etymons, but if you want to coherently use "heptante", which relies on a Greek etymon, you should probably also use "ennéante" in lieu of "nonante".
It's quite a shame, because that solution for reading hexadecimal numbers out loud is quite elegant :)