E4200 won't connect beyond 144mpbs

Question

Just got the router and set it up...
On the 2.4ghz side, I'm set up on the cleanest channel (per inssider) which is 6, channel width is auto (although I've tried it fixed at 20 also), N-only, and security is WPA2 personal.  WMM support is enabled.  I'm running firmware 1.0.02
The laptops continually stay around 72mpbs, occasionally jumping to numbers in the 100 range... twice I saw it actually hit 144.  Inssider shows the max rate as 144, while other N networks in range are as high as 270.  I'm sitting right next to the router with 5 bars -- why is the max rate 144?  Why won't it run at 300?

Answer 1

As you can see the 40 MHz network allocates channels 1-9 leaving little room for anything non-overlapping. In addition, you seem to operate another 11g access point. If in particular the 40 MHz generates a lot of traffic reverting back to 20 MHz seems a good idea. But as I wrote before, only actual measurements can give you a better answer.
All negotiated speeds have a specific set of parameters. 40 MHz is one of those parameters. You'll find a table listing all possible speeds here: http://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates
Please remember, that the connection speed is a theoretical boundary. It does not say how fast you can really transfer data. It only tells you which parameter where chose. They may change during a transfer. Thus make measurements. In general, you'll see only half of the connection rate or even less.
You cannot force the router to 40 MHz mode. Linksys seems to be very conservative with may configuration options which may cause complementary effects. I guess most users won't immediately understand why a connection on a higher rate (e.g. with 40 MHz) may have actual throughput then a lower rate (e.g. same parameters but 20 MHz). It doesn't help to force a router to 40 MHz to see a 300 Mbit/s connection but only 40 Mbit/s throughput while you might see 60 Mbit/s on a 144 Mbit/s connection with 20 MHz band.
Considering the amount of people which complain about the connections on the 2.4 GHz band and the observation that the E router often reverts to 20 MHz only may indicate though that they are too pessimistic with their choice to accept 40 Mhz or not.
As I wrote before, you may be able to see 40 MHz for a while directly after a reboot until the router receives too much interference and decides to go back to 20 Mhz.
Settings on the adapter are in the driver.