The Java simulation would be just as fast as the C one in the median case. The two problems with it are that 1) the big bang would have taken forever to start up and 2) the universe would eventually skip a beat for a stop-the-world GC cycle.
Not sure speed is relevant here. Those inside the simulation would not notice the difference, would they?
If the world is simulated then "real" time simulation speed does not have any influence on our experiences inside simulation. For all we know the next-up world can have different dimensionality from ours or no at all.
I'd prefer slow to "in the best case, everything blows up at once - in the worst, there's a memory error that if exploited, turns your world into a dystopia".
“There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
There is another theory which states that this has already happened.”