I wonder if the problem is with SOAP or with the design of Sugar and/or the Sugar API.
We will not likely switch to JSON, but there is an interesting debate going on:
http://ajaxian.com/archives/json-vs-xml-the-debate
I do believe that the problem does lie in the Sugar-Soap implementation. Some tests we've run show that when transfering large amounts of data there is an inordinate amount of time spent on the sugar server as opposed to transmitting or clientside. Unfortunately we can't, and don't really want to, get into that code to figure it out and optimize it. And, unfortunately, it was a trivial thing for our php programmer to implement Sugar's existing JSON functionality. So now it's up to me to write a web reference object that uses JSON instead of XML. The sad part of that is I have to totally scrap the really easy to implement (read ignore) .NET WebReference "bottled" code/object (SplendidCrm), because there doesn't seem to be a way to dictate the data transmital format. (please if you or anyone else knows how or where i should look on how to do this, I'm open to suggestion).
Oh, and that's a great reference page you had, many of those articles I've come across already but there were some others I hadn't. Great starting point for anyone trying to choose twixt JSON and XML. Unfortunately the argument of JSON vs XML is probably moot, Web Services should probably be written so that they can tell what they're getting and return the same, leaving the method choice up to the Client.
Louis