You're definitely asking the right question, and IMO the answer is "sortof." It's not that impressive in the grand scheme of DDoS, given major attacks will sustain 100 gigabit traffic[1] sometimes for days on end. But 20gbit/s would likely be enough to take down a small & unprepared business.
[1]: http://www.techworld.com/news/security/worlds-largest-ddos-a...