My comment was not meant to disparage your 270 - 216, I am stuck at 144. I have 3 different routers and have tried all of them. I use 40Mhz band width in the 5Ghz range, router is set to N only, AES encryption, everything that I am supposed to use, but nothing improves my speed. My only question is have you changed any hardware or settings on Surface because you are doing a lot better than I.
I just disabled IPV6 on my wireless network adapter and I am getting a steady 270Mbps. Machistmo, if you still have IPV6 enabled it would be interesting to see what you get by disabling it.