You repeated what I said regarding physics and monitor frame rate. I was just adding to the discussion because FPS really is a bad choice for an acronym in XML :)
Physics math run on the CPU only.
The CPU usage can be barely none or more intensive. Academic stuff: same amount of stuff to to will generste more load as you have to run it more times.
Point is not that. Point is, although you can use lower rate for physics, you'll also have less accuracy, obviously.
Plus, like I said, newton engine used by FP, alters objects weight starting with the ball.
You can probably find post from me here pasting Rafal answer to one of my questions about this via email a long time ago. I won't discuss this further because I don't have a full list either. Just trust on this because this was tested by me and JLou (and many others over the years I'm sure) but also because it was Rafal writing it :)
And since FizX was create with some basis in mind, like I said, you should use 512.
It makes a difference, especially at higher frames rates and as in all simulations you are already at a disadvantage if you have to run under optimal settings. The feel is quite obvious for me.