I currently get a max of 333Mb down speed through my RT N66U. (Ethernet) This is the Max allowing for overheads in my SH3 Config file. I have no reason to believe that when VM boost me to 350Mb that I wont get 360Mb or more.
Check that your firmware is up to date and that all your ports and switches are capable of gigabit speeds and that any connecting cable is Cat5e or better.
I also get over 300Mb using WiFi in the same room as my N66U.
Ethernet, but with 3 other users currently on line in the house.