It's a silly tip, but if you don't know it you will find this useful. While exploring the official .vmt Valve maps you will realize that your fps on the 3D camera will go down (a lot!). You will realize that most of the Valve map face textures are nodraw. So if you want to increase your fps rating on the 3Dcamera press the nodraw button at the top right of the screen, uncheck the displacement sprites too (will help, but not so much. Hammer don't have to render the nodraw faces (almost all the map) so now you should have an acceptable fps.