Newer JVMs are faster, but you should create your own tests for your particular application to understand the difference. Many times, performance is satisfactory on an older JVM, and so why switch?
You know, you cannot just say "newer are faster" for sure...I asked becouse I haven't done any perf tests and I would like to know that switch to 1.6 is worth.
Why not to gain almost free speed up? :))