We do expect some performance degredation when running XPath against a DOM, since we now have to build the DOM2DTM proxy layer and that can introduce a significant amount of overhead. The tradeoff is that switching to being based on DTM was expected to significantly improve stylesheet performance.
It may be possible to come up with another version of DOM2DTM which is better tuned for XSLT, since our DTM encapsulation has gotten a bit better recently. Let me think about that...
