I just got 5 gigabit internet from AT&T, what can I do?

You might want to re-read your contract to verify you're allowed to run a server on that connection (and AT&T will consider both a Helium node and a Tor relay to be a server).

I honestly have no idea what a 5Gbps connections could give you over a 1Gbps. I have the Google Fiber 1Gbps service and the only things I can do to saturate the connection are: Speedtests, downloading something from Bittorrent, pulling down 500MB driver files from Nvidia (though I haven't tried that since I first got fiber service 8 years ago). Google wants me to upgrade to 2Gbps service for $30/month more but Google's own services don't run faster than about 150Mbps so no.