Hi,
I followed the steps provided by you and updated the Wi-Fi driver, in Device Manager is showing now N-6205, surprisingly the speed is gone up with 6Mbps, from 8Mbps under N-6235 to 14-15Mbps, yes there is an improvement.
The real speed I expect to be around 20Mbps, but nearly 15Mbps is quite good (6m far from router through on wall)