Thanks for the replies everyone. Unfortunately, none of the console commands work; I tried setting speedmult to a ridiculous value (-500) and it had no effect. I verified it was set to -500 using getav. BYOG is a cool mod, but it too had no effect despite being last in my load order. I am not sure why I cannot change this--the vast majority of my mods are for visuals. Only two mods have worked so far, SkyrimSpeeds and Immersive Motion. However, SkyrimSpeeds changes every actor and Immersive Motion breaks a good number of my mods. In the end, I will probably disable those mods and just use Immersive Motion.