To get the best possible speed you also need to use WPA2 with AES
encryption with the wireless N only
setting in your routers wireless set up page.
You also need to use those settings in the Windows wireless connection manager as shown in the pictures below.
If you plan on streaming movies wirelessly you will also need to make sure that the wireless channel isn't being used by one of your neighbors. This is a very important step in order to get movie's to stream wirelessly. Xirrus WIFI inspector works well for this. http://www.xirrus.com/Products/Wi-Fi-Inspector
300Mbps is what you should be seeing if everything is set up correctly.