Check out that link I provided - it gives information about the alleged 300Mb/s windows link.
Good link but not new information. The point is that I get a "real measured" 4x speedup xfer rate when the 802.11n link runs at "full speed". After searching around abit, it seems the linux drivers and wireless tools like iwconfig are not able to activate the 802.11n speeds. For instance, iwlist reports speeds that max out at 54Mbps for my dwa-652 (AR5008 adapter).
Not sure what you mean by not new... that is from Feb this year. The table in Q1 shows maximum speeds in perfect conditions. The side bar to the right shows the wireless performance leader board - Buffalo Technology WZR-HP-G300NH average throughput at 48Mbps.
The latest review, a "300MBps" EnGenius router he measured a maximum of 60.9Mbps single direction and some 74Mbps both ways simultaneously combined total.
your measured 308MB per 60s is 41Mbps. That is typical n class speed. And so is 54Mbps. But perhaps that 54Mbps reported is a sort of 'marketing' speed, and that the actual useful speed is a lot lower.
So perhaps your wireless link is not running full speed despite being reported at 54Mbps... I have no way right now to test mine.
Anyway, I am still sure you can safely forget about actual 135Mbps.