I have just bought a Vaio Pro 13 with the N 7260 card and made an upgrade to Windows 8.1 pro. I As soon as I install my VPN (IPSec) client software (made by AVM, but the shrew soft client produces the exact same result) the adapter does not connect on the 5GHz band. It still connects on the 2.4 GHz band without restriction and it also connects on 5GHz if I enable FIPS compliance but it is then restricted to 54Mbps.
This really bothers me because I need the VPN client software and I also need the bandwidth. On my old Vaio Z with a Intel WiFi Link 5100 AGN there is no problem at all (Win 8.1, same VPN client). So it must be down to the driver. I use the latest ver. 16.6.2.1. You need to fix this.