Performance of SOAP vs. XML-RPC or REST

Solution 1:

The main impact in speed of SOAP vs. REST has not to do with wire speed, but with cachability. REST suggests using the web's semantics instead of trying to tunnel over it via XML, so RESTful web services are generally designed to correctly use cache headers, so they work well with the web's standard infrastructure like caching proxies and even local browser caches. Also, using the web's semantics means that things like ETags and automatic zip compression are well understood ways to increase efficiency.

..and now you say you want benchmarks. Well, with Google's help, I found one guy whose testing shows REST to be 4-6x faster than SOAP and another paper that also favors REST.

Solution 2:

REST as a protocol does not define any form of message envelope, while SOAP does have this standard.

Therefor, its somewhat simplistic to try and compare the two, they are apples to oranges.

That said, a SOAP envelope (minus the data) is only a few k, so there shouldn't be any noticeable difference in speed provided you are retrieving a serialized object via both SOAP and REST.