Both will work the same since it is unlikely the routers you attach to will support these features.

To support the most customers people who run open or pay internet wifi set it to run the most common settings. Many people will not even have N so it is likely you will end up running G anyway.

The 300 and especially the 450 are not common features. These are hogs when it comes to radio bandwidth. If they follow the rules most will disable the feature themselves if they detect other routers on adjacent frequencies. It is rare to not find routers on all frequencies all the time. Many people override this setting if they want to use this in their house.

Range and coverage are related to transmission power. Many transmit at maximum legal power but some transmit lower to reduce the battery drain on laptop.

I would actually look at a external USB card. It gives you the option to put the device on a USB extension cable and place it where it gets the best signal. Avoids the problem of having to place the laptop in a strange working position to get enough signal.