I'll just throw in my datapoint on this subject because it might be of interest. My relay (torpoint) is currently advertising a
bandwidth of 58 MB/s according to Globe. Arm reports that it is pushing 50 MB/s and has 12,500 open clients.
It has a Xeon E3/1220 with 8 GB ram. The load average is 0.75, and the four cores are at about 20-25% each. About 2GB
of ram is being used.
On the whole, this relay is probably bandwidth constrained. The ISP guarantees 150 Mbps, but I sometimes get more, like now.