How about WCF for large amount of clients and large amount of data?

Does anyone have statistics of using WCF with 20000 clients?
just don't know it's performance of loading 20000+ clients, anyone can give me a real data about this?
and also, for each client, we will transfer data from serveral Kb to 100MB, does it suitable for WCF to finish this in a good performance?
and also, is there any messaging platform good enough for us to use with low cost in money?
just need purely .net platform. Would anyone give me some lights on this? thx very much.

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