Measuring speed with iwconfig seems to be a bad idea. On my computer with similar hardware (tpx220 + intel wifi 6205 + 5 ghz router) i get different results shortly after another. Example: iwconfig #1 Bit Rate=6 Mb/s Tx-Power=15 dBm iwconfig #2 Bit Rate=243 Mb/s Tx-Power=15 dBm iwconfig #3 Bit Rate=270 Mb/s Tx-Power=15 dBm The bit Rate keeps changing every measurement, it is usually displayed higher after loading a web page and at 6 Mb/s when idle. Since you are on similar hardware, can you post your kernel version, and the output of lspci -nnk?
Intel Centrino Advanced N 6250 Driver
Intel(R) Centrino(R) Advanced-N 6250 AGN Drivers Driver Information Old drivers impact system performance and make your PC and hardware vulnerable to errors and crashes. Downloads for Intel® Centrino® Advanced-N + WiMAX 6250, Dual Band. Download type. Any Download Type. Identify your products and get driver and software updates for your Intel hardware. Description Type OS Version Date; Drivers for Discontinued Intel Wireless Adapters. Drivers for Discontinued Intel® Wireless.