Concurrently downloading JSON data from remote service(s)
Might be related to the concurrency mode of your service. Check http://msdn.microsoft.com/en-us/library/system.servicemodel.concurrencymode.aspx and make sure that the service is not single threaded.
The best answer to this question I ultimately came up with came from this link:
Which applies if you are calling the same servive method repeatedly.
By tweaking ThreadPool.SetMinThreads() on both client and server I was able to get improved results.
However there are still alot of slowness issues with WCF and transferring over HTTP that I haven't really gotten to the bottom of.