SOAP is only worthwhile if you're using advanced features of SOAP and require the language-interoperability that comes with using XML. SOAP is necessarily slower than other forms for communication (because XML is a larger data type and because SOAP is so feature-bloated), and it also suffers from the overhead of encoding/decoding XML (if you were to do that, I'd use XML::LibXML, which is clearly the fastest perl XML parser so far).

If you need the language-interoperability of XML but are only doing simple key-value interaction, use XML-RPC. XML-RPC is basically (very basically) cruft-less SOAP. Check CPAN for available modules (RPC::XML and Frontier::RPC come to mind). Even SOAP::Lite, the most feature-laden perl SOAP module comes with an XML-RPC version of its basic use.

If you don't need the XML sort of interoperability (say, both ends of your application are perl-based), roll your own server-client app very simply using sockets and Storable. There are CPAN packages that enable you to setup very simple servers with minimal hassle, and Storable is very speedy for packaging up data and shipping it across networks.

95% of the time, SOAP isn't needed. I used to know of a great article that outlined why XML-RPC should be used over SOAP most of the time, but I can't find it. Your case doesn't even sound like XML-RPC would be necessary.