802.11n to 802.11ac upgrade network card

There are two reasons people want to switch out their AirPort board to gain performance and/or to gain Hand-Off.

802.11ac performance: If you are expecting big improvements in throughput you may find it isn't much as you had expected. Depending on where the remote system is located, the bandwidth of your AP and the network between. And lastly, how congested your air space is as well as the band your AP is setup on.

Also remember the 802.11ac AirPort card is limited by the antennas in your system. You can't leverage MIMO as you need an additional antenna which is not present in your system (current card has two WiFi the newer card has three WiFi connections). The AirPort card you need is a Broadcom BCM94360CS2 card

Hand-Off: Here is the best source of info - Continuity-Activation-Tool