Getting max speed depends on many things. Some routers/adapters use the channel width to get max, others use dual-bands to do it. It all depends on the equipment you are using and the environment in your location. The best way to get max is with matched equpment. You may be able to get max in a G/N environment but some will see lower speeds. Alot of it is luck of the draw. If you are in an area with alot of interfernce you may see lower speeds. 300 is also just a theoretical number, everyone's experience will be different.