Take a look at XML::FromPerl, which provides an easy way to generate XML form Perl using XML::LibXML under the hood. I have no idea how fast it is, though.
Comment on Re: Replacing XML::Simple XMLout with Lib::XML
I've just had a quick look at the source and its not a million miles away from what we've done; but it does rely on a particular structure of hashref/arrayrefs that we don't have so we couldn't use it as it stands but its reassuring to know at least one other person took the same approach.