I've run XSLTMark on my own, comparing the XSLT 1.0 compliance and performance of Saxon (Java), Sablotron, LibXSLT, and Xalan C++. Sablotron 0.70 - the latest version at this moment - fails on several tests, which indicates that it isn't fully XSLT 1.0 compliant, and the performance is not impressive. The rest of them - LibXSLT, Saxon, and Xalan - are fully compliant. And among these, LibXSLT is undoubtedly the speed demon. Xalan is the second.
But if you're afraid that at some level of complexity you can't deal with XSLT alone (or it's too complicated to solve in XSLT, see Things XSLT Can't Do), you may try XML::Xalan, the perl binding to Xalan C++. It allows users to write an XSLT extension function in Perl. I know it lacks of several features, such as document validation, but currently it serves my need very well. Untested on Win32, though, just on Linux only.
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