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".

In the context of hex numbers "quatre-vingt" isn't a problem tho, no ambiguity.