A really good CDN like Steam can absolutely saturate a link like that. I'm on a gigabit line (which actually performs at more like 1.1), and I've seen 120MB/sec download speeds on Steam. With today's games often weighting in at 50GB+ that's not nothing, either.
Steam won't ever saturate my 2400Mbps line but it will absolutely exceed 1000 for sustained periods. Microsoft is slower but updates and Xbox games also hit 1000 sometimes
