Bell 2 wire modem and router

[kulkulkan]

I have Bell's Fibe-12 which comes with their 2 wire modem with built-in G router. I am able to get 11 MBps, wired or wirelessly which is close enough (probably more than 12Mbps at demarc point) but the range / signal strength isn't very good throughout the house (given G-router).

So, I decided to try another router (Dlink Xtreme N 655). I disabled the Bell G router and put it in bridge mode, and connected D-Link router to it, but for some reason my bandwidth cuts into half (5 Mbps) - doesn't matter if the test device is wired directly to D-link router or wirelessly. I also tried another D-link G router and same result (5 Mbps). With the built-in Bell G router, I am able to get 11Mbps (wired or wirelessly).

Any obvious reason why this is happening and what can I change to get the full bandwidth on the D-link router (or any other N-router that I should consider)?

Thanks for any suggestions. Bell online tech played around with their modem / router with no change in results but it didn't seem like she knew what she was doing.