Wow thanks for the tips! I was definitely struggling to make it run nicely. Though it was only in my code but failed to think about the impacts of all those collisions. Will try to add your solution to make it more playable
your welcome, your case interested me so i tested, and i made a mistake, it's not about the dynamic speculative, it's in the interpolate mode, basically you keep the rigidbody discrete, and the interpolate make a smooth lerp between two physics update, allowing you to lower the number of updates, of course it's not great looking if you look close but that's not important in your case, if you wonder, in my pc i managed to run more than 8000 cubes at the same time with a decent fps