I am based in Germany. I have recently got a new 100 Mbit/s internet connection.
My new Router is a Fritz!Box 7490, with Wifi speed 1300 + 450 Mbit/s in 2.4 and 5 GHz.
My wireless network card in my desktop PC is a TP-Link TL-WN781ND WLAN PCI-E Adapter (150Mbits/s, Windows 8.x / Vista / 7 / XP) , with up to 150 Mbit/s (so, still 1.5x the speed of the internet that comes out of the wall).
Now, when I use an ethernet cable to connect the PC (Windows 8) to the router, the download speed is approx. 11 MByte per second, so very close to the 100 MBit maximum. The Ethernet cable goes into the mainboard, an ASUS Z97-K.
The same computer, download applications, etc. only achieves approx. 6 MByte/s when connecting to the router using Wifi.
I also used a directional Wifi-Antenna directed at the router, with no improvement. However, the PC and the router are just 3-4 meters from each other in the same room anyway.
As far as I can see, all hardware should be capable of achieving speed well beyond 100 MBit/s, therefore the bottleneck for the Wifi speed should be the internet speed "in the wall", and not any of the Wifi-hardware between the wall and my PC.
What can be the reasons, and how can I improve the Wifi speed?