I did a bit of performance testing, comparing jAMOS to AMOS Professional running under WinUAE (with Direct JIT + Fastest Possible CPU, 8MB Fast RAM, ECS chipset, hardware collisions disabled).
For the Mandelbrot plotter (on my i7 machine), using almost identical code and producing identical output, jAMOS performed 8 times faster than AMOSPro in WinUAE using the AMOSPro interpreter, and around 4-5 times faster than the AMOSPro Compiler. (Bear in mind that jAMOS uses 24-bit plotting and an interpreter running on a JIT-compiled Java VM.) Both maxed out one hardware thread out of 8, i.e. half a physical CPU core.
Of course this is still pretty slow for a Mandelbrot plotter (it took over a second to draw a 720x576 image in jAMOS on my i7), but already has major performance gains over emulated AMOSPro. If I have time I'll add the ability to compile jAMOS code to Java source compilable to Java bytecode, which should improve performance some more.
Sprite and screen display in jAMOS is still quite sluggish on slower PCs however, due to its somewhat inefficient usage of JGame's sprite engine at the moment. The sound engine may also cause occasional freeze-ups due to the JVM heap size being too small and forcing garbage collection. This can be fixed by launching jAMOS from a command prompt and specifying a larger heap size using JVM command line options.
From my tests, its interpreter is surprisingly nippy though, as is its AMAL interpreter.