I never have problems with WiFi in the Surface, now, my 5Ghz band is weaker than the 2.4Ghz which is also normal but I find that it's a little bit weaker than what I think it should be considering the distance between the device and the AP.
Anyway, when I got the Surface and I connected via the 5Ghz band and I found what I just described I went and did what I usually do in all my PC, optimize the TCPIP settings. I was not expecting to find a version of TCPIP Optimizer for WinRT so I did a search in Google for TCPIP optimizing hacks and I found this page:
Using a DOS windows with elevated privileges you can apply almost all the recommended settings there.
Taking in consideration that I did this with my Surface almost right out of the box and that I have only seen the "limited" message issue one time connecting to my phone using it as hotspot in an area with a very poor 3G reception, I'm inclined to think that may be that some of the settings mentioned in the above link may help with some of the issues described here by other users.