Here are some of the sites that I have really found good and informative about the different performance reports for 64-bit platforms (from a MS technology centric perspective).
64-bit Performance Benchmark: .NET 2.0 and IBM Websphere 6.0 - http://msdn.microsoft.com/vstudio/java/compare/benchmark64/default.aspx
XML performance showdown: Java, Mono and .NET - http://www.process64.com/articles/xmlmark1/xml-mark-revisited.pdf
Performance figures for 64-bit Paint.NET v2.6 - http://paintdotnet.12.forumer.com/viewtopic.php?t=651
Demo of the paint.NET application on different platforms
Performance comparison of Java (and .NET) runtimes - http://gcc.gnu.org/ml/java/2004-10/msg00099.html
HPC.NET – are CLI based Virtual Machines Suitable for High Performance Computing - http://www.sc-conference.org/sc2003/paperpdfs/pap251.pdf
In case you know of more, pl share the same.