It's not the adapter's fault but Sony Vaio Pro's antennas or poor driver performance on Windows 8 since on my Lenovo G470 Windows 7 laptop with Wireless-N 7260 16.1.3.1 drivers, I get 81Mbps download and 39Mbps upload on my university campus Wi-Fi using speedtest.net
Also, you have to set the channel width on 2.4 GHz to "Auto" on the advanced adapter properties.
Follow this link for optimum performance: Wireless Networking; What are the recommended settings for 802.11n connectivity? ,
Wireless Networking; How to configure 802.11n channel bonding on Intel Wireless adapters