2000 will be a bit laggy, i'd say 1600 is the absolute max you can get away with without decreasing framerates or increasing ping. Of course, it's affected by how much you can see at any one time, if it's an indoor map with rooms connected by corridors, it'll perform better (and you can get away with more) than an open-air level where you can see the entire map at once.
Remember than a lot of faces are used in detail, and there are other ways to detail your map. Large, decent textures and env_models can be lifesavers.