Let me state the problem. My ISP provides a 60mbps connection to my place. The router is set to abgn mode (to support older devices to) and runs on 2.4GHz.
I've got few devices that are connected to that network and some of them do support at least 802.11n standard. Below are speedtest results for them:
There's no way I could get anywhere near the speeds of my Mac on my PC if it comes to the connection. It's always around 20mbps. I did try with different USB WiFi cards (both from TPLink in 802.11n standard) but it was the same.
Try these articles:
http://www.intel.com/support/wireless/sb/CS-030709.htm Wireless Networking — What are the recommended settings for 802.11n connectivity?
http://www.intel.com/support/wireless/wlan/4965agn/sb/cs-025643.htm Intel WiFi Products — Data rate will not exceed 54 Mbps when WEP or TKIP encryption is configured
http://www.intel.com/support/wireless/wlan/4965agn/sb/CS-028449.htm Wireless Networking — How do I improve my 802.11n wireless performance?