BT unstable, intermittent, cutting out, may/may not come back to life on a reboot etc.? This card fixes this. As I mentioned, one of my 2012s suffered this while the other had identical WiFi non-performance.
Per the Wiki article, the 802.11ac specification has multi-station throughput of at least 1.1
gigabit per second (1.1 Gbit/s) and single-link throughput of at least 500 megabits per second (0.5 Gbit/s) — the spec was finalized long after Apple started shipping. Apple boasted 1.4 Gb/s when it was released in 2013 and my son-in-law said that they achieved that regularly in testing.
The only way to test actual 802.11ac performance is in a clear line with a PC or Mac with the same and not through a router (don't have a water heater in the way—just sayin'). When sending 100GB files and timing them, comparing to Gigabit Ethernet, I don't quite achieve 1.4 Gb/s but I get close and it is faster than Gigabit Ethernet.
Most home internet connections are not nearly that fast. Neither WiFi nor Ethernet can connect to the internet faster than your connection to the rest of the world.