What I have been doing is as follows

I create a new top-level page (next to home and other top level navigation)

I give it's visibility permission to only the people that are premium or pro roles, so that way only those logged in, with the required role can visit or even see it in the navigation

Under this top-level page are all my sub-pages, this premium/pro members only area, I apply all the permissions to the subpages of this top-level page

I determine which modules can show content to both premium and pro, which modules can appear only to pro or only to premium, and I tediously go through permissions on each module so it will be hidden to one role and visible to the other, or visible to both if its okay to show both.

It's working great so far.