Oh! there's a "speed" setting? I'm not sure where that heart is that you're talking about.Yeah, it gets a bit silly on max speed, best works on middle settings (heart at the top of the screen is speed scale). Perhaps lowering jiggle in the character creation (effects tab) will fix it for the max speed?
I'm messing with the phsyics sliders again, and now I've successfully turned them off. but I noticed that when I adjust the body settings ( like when I adjust the fat skinny or muscle settings ) I can't actually go back to the normal settings. Even when I click on normal, the sliders are showing the wrong ones. That must have been what was tripping me up. There's definitely some kind of bug.