[imtringued]

>For example, just measuring the impact of GC overhead is bound to be tricky, because a trashy program (one that allocates a lot of garbage) is going to make GC look bad in comparison to a program that is careful to reuse data structures.

This is completely irrelevant because stop the world pauses are global and affect your entire application no matter how careful you write your code. Every library you use has to be carefully written, every single line of code you write has to be carefully written regardless of whether it is time critical or not, this is a complete dead weight for the entire application.

With isolated GC heaps your time critical code will be isolated from non critical code. In practice the easiest way to do this is to just launch a separate application. This hurts a lot with the JVM because it wants to own your entire server (mostly RAM) for some inexplicable reason and you might as well write that part in C++ if you do inter process communication anyway.