Poisoning skill also affects the strength of spells that poison. So a beetle with higher poison should have a more effective poison spell, and I'm pretty sure I've seen this in action.

You mean like Eval to Curse spell? Damage over time is relegated by poison level (1-6) as is duration if the target does not cure it...

When you cast a poison spell, whether it is a poison field, or the poison spell itself, your poisoning skill will affect how strong the poison is, I believe both your poisoning skill and the range your are from your target affect the strength of the poison. The same I believe applies to rune beetles when they cast the poison spell. At least this is the way it used to be five years ago, and I don't think this has changed. That's what nox mages are all about.