Douglas wrote
You can use as many clients as the 500 Mbit/s will allow; however, that doesn't mean all of your clients will saturate their local connection. Some will get poor speeds some will get better.
Besides that, i.e. custom ADSL-providers share their bandwith with 20 ~ 50 more customers then their bare bandwith (overbooking). Accounting this on your server, you could 10 ~ 25 times "overbook" your server. (Take care: data has to travel twice through your server, once as upload and once as download!)
Having said that, pushing 10k users (that is, selling roughly 25 mbit per user) through a single server will definitly give you problems with cpu-load, filedescriptors, memory-allocations etc.
Cheers,
Max