AMF::Perl is definitely the right way to go. It is possible to get Flash to handle XML now but this has two drawbacks which totally kill performance: Flash is not that fast when it comes to XML processing and it does not support the mod_gzip 'compressing XML' tricks which may have saved it.
Overall expect remoting to be at least 3x as fast as XML when dealing with Flash. The fact that AMF::Perl is just so simple to use only adds to the case.
Note the recent Flash 8 release doesn't have the required Remoting components built in, but they can be
downloaded and installed fairly easily.