XML::Twig is great if you need a pure Perl module, but XML::LibXML will produces results much quicker
XML::Twig is no more Pure Perl than XML::LibXML. Both use C libraries to perform the parsing. It's possible that XML::LibXML is faster, but it's not related to the choice of programming language.
XML::LibXML [...] isn't as memory heavy.
That's an odd thing to say. The whole idea of XML::Twig is to keep nothing in memory that doesn't need to be, whereas XML::LibXML keeps the whole document in memory.