there are some public studies on DDOS size over the years. IIRC Arbor networks published some numbers earlier this year. IME tens of Gb/s is a mid size attack these days. Large is a hundred plus Gb/s.
I can't find any public reports topping ~100 Gbps. For example, here's a recent article that interviewed an Arbor employee and mentions a ~100 Gbps plateau:
Hrm, maybe Im misrembering. Found akamai claiming 125Gb/s in '09, and some more arbor quotes of ~110Gb/s. I'll see if I still have the report Im thinking of tomorrow.
http://www.techweekeurope.co.uk/news/ddos-attacks-power2012-...