{My apologies for not having been logged in earlier when I suggested XSLT}

As you said: "source XML is large" and contains "non-essential information". His example case was "large" (3.3MB) and searching solely for tags of type <message>. That is a very simple XSLT to output as HTML (fragmentary example, please don't carp about the syntax):

 <ul>
  <xsl:for-each select="message">
   <li><xsl:value-of select="current()" /></li>
  </xsl:for-each>
 </ul>
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XSLT can convert XML directly into XML, HTML, or even perl:

 @messages = (
               <xsl:for-each select="message">
                 "<xsl:value-of select="current()" />",
               </xsl:for-each>
             );
[download]

I wouldn't want to comment further without a better understanding of the actual "processing" to be done, but the simple example presented in the question is practically a textbook case for XSLT.

Whatever. Use the tools you like.