I've just had my home internet upgraded to 50Mb/s down, but I can only get about 25 Mb/s down on my laptop over wifi. My phone gets about 45 Mb/s down over the same wifi and I get the full 50 Mb/s down when connected via Ethernet cable to the router, so I'm fairly sure the problem is on my laptop.
03:00.0 Network controller : Intel Corporation Centrino Advanced-N 6205 [Taylor Peak] [8086:0085] (rev 34)
This makes me think that for some reason iwlwifi isn't driving the card as hard as it can go:
mwhudson@narsil:~$ iwlist wlan0 rate wlan0 unknown bit-rate information. Current Bit Rate:54 Mb/s
(The card can do 300Mb/s according to Intel's pages, as can my router). I see similar performance on the 2.4Ghz and 5Ghz bands (my phone only does 2.4Ghz).
I'm running up to date Ubuntu Saucy.