No worries about this. There's no real maximum number of gigs. This notion is odd to us. Nobody is abusing a network doing 500gigs off peak, and we hate the term abuser in any case.
Let's take two uncapped customers on the same product and same price:
Customer A downloads 500GB between 11pm and 7am because that's when automated downloads fire off in any case and when stuff is released. He occasionally streams and games during the day.
Customer B downloads 200GBs but all in daytime peak usage.
Customer B has more of a detrimental impact on our network than customer A, even though customer A downloaded more. We calculated peak capacity on unshaped and then ran some complex forumulas to determine how much of this peak usage we actually "don't care about" or at least can provision capacity for in ADDITION to increasing bandwidth priorities to high once shaped. We added margin to cover costs and every second Tuesday buy some bread and milk, and priced the products.
So it's more about what your unique usage patterns demand of our network. Not of how much you use overall.