How to use permission groups to filter user options?

If you are talking about a dropdown list with options visible depending on the permissions of the user, you could create another custom list and store your "options" in that list, then apply permissions required at an item level in that list

Item A - Owners, Members & Visitors

Item B - Owners, Members & Visitors

Item C - Owners & Members

for example

Then using the list lookup control, point at this list and configure as required. When a user belongs to the Visitors group, they should only see Item A and B in their drop down list.

Does this solve your issue? If not please give more details on what you're trying to achieve.

To make sure I've got this correct, if you were a Visitor in this instance then you wouldn't see Item C? I believe this is the approach I took but I want to make sure I am understanding this. 

Thanks

Yes, Nintex adheres to the SharePoint permissions, so if a user doesn't have access to an item they won't see it.

If this resolves your question, please mark it as correct. Thanks