Definitely keep your models and textures on high, lowering them will cause more issues than good and doesn’t really have massive benefits with modern hardware for a two decade old game, you are best off just tuning what you can in the F1 options, like turning off the 3D skybox rendering and putting -high in your Garry’s Mod launch options will put it in high priority mode from the moment it launches, which is great for a more CPU bound game
There’s a nicely written guide by one of the community members you can look at too if you’re trying to milk as much FPS you can but there is only so much you can do before it’s just simply a case of get a better PC.
Fixing PERPheads on Windows: The Complete Launch Options & Performance Guide
Before I start, I don't exactly know how helpful this will be to users, and I don't know if people even care, but I had alot of issues when I used windows so here it is :3
Freezing around the Bazaar, sudden frame drops during police chases, and out of memory crashes are constant issues on Windows. Alot of players try to solve this by copying decade old launch option strings that definetly do not work on modern systems.