A user of Saxon on .NET, Don Burden, has been doing some performance tests:
At first sight the figures are not especially good: 227 transformations per second against 613 for the System.Xml.Xsl transformer. However, closer analysis shows that a great deal of the cost is in converting the System.Xml DOM into a Saxon tree prior to performing the real transformation. This isn’t really a surprise - the API documentation contains some clear warnings about the cost of doing this (it’s far better, when you can, to build a native Saxon tree directly from raw XML - the same is true for the Java product).
As would be expected, there is TONS of fantastic information contained in this entry from Dr. Kay. If you are a .NET developer who uses XSLT to any great extent, or a Java developer looking to expand your horizons while building from your existing Java code-base, this article is an absolute must read!