The newest iMac 2013, MacBook Air 2013, MacBook Pro Late 2013 and AirPort Extreme / TimeCapsules are all compliant with the new high performance 802.11 ac standard. (on a side note: unfortunately unlike the new iphone 5s/5c, iPad Air or iPad Mini Retina).
The biggest problem users are facing is to identify if their new equipment is really ‘talking’ ac or if they are still in n-mode.
A click on your WiFi icon in the menu bar is showing only the connected network (in this case TAURUSGEMINI) and the signal strength but no further details.
You have to click on the WiFi icon altogether with holding down the alt-option key to see a more detailed view.
And most probably you will see (with a standard out-of-the-box-installation) something disillusioning like the below, showing you that the expensive equipment you bought is still using the same connection speed than hardware you could have bought for half of the price.
You probably have looked everywhere under System Preferences/Network, and throughout the AirPort Utility application but you couldn’t find any place to select 802.11 ac as the preferred network standard. Furthermore what would happen to your old n-only compliant hardware in case such an option would exist?
It is important to know that 802.11 ac will only operate in the 5 GHz radio band. As such you have to configure your router accordingly. 802.11 can use as well the 5 GHz radio band but not necessarily all end devices can access that band.
On a new generation Airport Extreme and Airport Time Capsule you can configure under Wireless Options a different SSID (Network name) for your 5GHz radio band.
With this little and simple setting you can ensure that your ac enabled devices will definitely always connect to your high speed (802.11 ac enabled) radio band.
A quick option-click on your WiFi icon in the menu bar is now showing that indeed high speed connection is used all the time.
As of now there are only a few devices able to use ac it is perhaps useful to make this 5GHz network hidden, as such all your 802.11 n connections will be routed through the 2,4 GHz radio band and you have the 5 GHz radio band reserved for 5 GHz connection only.
However has we have to face different physical signal penetration depth for the different GHz bands this is something you should play around a bit. It might well be that the 5 GHz radio band will help you in getting a better and stronger connection for your legacy 802.11 n equipment.