How Much Faster is Java on a 64 Bit AMD Opteron?

Just read the official announcement, "Sun plans server with AMD's Opteron". In that article Jonathan Schwarz alludes to something like this:

64-bit version of Java shows performance improvements over the 32-bit x86 version

I'm not sure if he's referring to Itanium here, however, what I want to know is "How fast is Java on a 64-bit AMD Opteron processor?". Could someone at Sun or SUSE clue me in on the details?

There's much stuff I can find about this on the web. Nevertheless, I stumbled on this from the makers of the 100% pure Java FirstSQL database:

FirstSQL/J Enterprise Server on 64-bit Itanium2 Benchmark results % increase over 32-bit are as follows:

Performance Increase:--Disk Mode---------In-Memory Mode
Simple Inserts------------14%-----------------18%
Complex Inserts-----------35%----------------56%
Simple Query--------------34%----------------22%
Complex Query------------- 7%----------------13%
Complex Inserts/Query-----20%---------------13%

Of course it isn't clear what it exactly is being compared against other than a vague mention of a 32 bit x86 machine. So until someone gets an Opteron and runs both 32-bit Java and 64-bit Java and makes a comparison, 64 bit implying faster remains as conjecture.

[UPDATE] An anonymous reader points out these SPECJbb2000 Opteron benchmarks from ACE hardware. Impressive, but I've got to point out that they were running a 32-bit JVM (i.e. JDK 1.4.1 ).