My file server is running Ubuntu 12.04 and I'm sharing files from it over samba. It is connected via gigabit ethernet. My desktop, running Windows 8.1, is also connected via gigabit ethernet. I can transfer files between the two and completely saturate that gigabit pipe.

However, I just got a Surface Pro 2, and I'm trying to stream HD movies from my server to the device over WiFi. For some reason, I can't break much past 1.5MB/s transferring files over the network. I've tried streaming through XBMC and a standard file copy; no difference.

To add the confusion, if I connect to my guest network and then use my VPN server (installed on the router) to access the file server, I get around 3.2MB/s.

I've been running diagnostics to determine the root and I think I've found it but I have no idea what is causing it or how to fix it.

Router: Asus RT-N66U

Surface Pro 2 Network Card: Marvell Avastar 350N (Driver 19/09/2013 v14.69.24044.150)

InSSIDer: Link Score: 100 Co-Channels: 0 Overlapping: 0 5GHz Network Channel: 48+44

iperf File Server as Server; Surface Pro 2 as Client - TCP

Performance: Acceptable

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 192.168.0.90 port 5001 connected with 192.168.0.56 port 57367
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0- 1.0 sec  10.1 MBytes  84.7 Mbits/sec
[  4]  1.0- 2.0 sec  10.4 MBytes  87.6 Mbits/sec
[  4]  2.0- 3.0 sec  10.6 MBytes  88.8 Mbits/sec
[  4]  3.0- 4.0 sec  10.7 MBytes  89.5 Mbits/sec
[  4]  4.0- 5.0 sec  10.1 MBytes  84.4 Mbits/sec
[  4]  5.0- 6.0 sec  10.2 MBytes  85.8 Mbits/sec
[  4]  6.0- 7.0 sec  7.04 MBytes  59.1 Mbits/sec
[  4]  7.0- 8.0 sec  10.8 MBytes  90.2 Mbits/sec
[  4]  8.0- 9.0 sec  10.6 MBytes  89.1 Mbits/sec
[  4]  9.0-10.0 sec  8.62 MBytes  72.3 Mbits/sec
[  4]  0.0-10.0 sec  99.2 MBytes  83.1 Mbits/sec

iperf Surface Pro 2 as Server, File Server as Client

Performance: Poor

------------------------------------------------------------
Client connecting to 192.168.0.56, TCP port 5001
TCP window size: 22.9 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.90 port 40233 connected with 192.168.0.56 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  1.0- 2.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  2.0- 3.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  3.0- 4.0 sec  1.25 MBytes  10.5 Mbits/sec
[  3]  4.0- 5.0 sec  1.62 MBytes  13.6 Mbits/sec
[  3]  5.0- 6.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  6.0- 7.0 sec  1.38 MBytes  11.5 Mbits/sec
[  3]  7.0- 8.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  8.0- 9.0 sec  1.50 MBytes  12.6 Mbits/sec
[  3]  9.0-10.0 sec  1.62 MBytes  13.6 Mbits/sec
[  3]  0.0-10.1 sec  15.0 MBytes  12.4 Mbits/sec

For some reason, it gets capped and I haven't got a clue why.

Any suggestions?

Edit: My link speed is reported as 270Mbps by Windows. I'm less than two metres from the router with a clear line of sight.