I have a Linksys E4200 router with about 10 computers connecting to it. I'm looking for a way to monitor bandwidth usage in real time. I am willing to install custom firmware if it can get the job done. It seems bandwidth is leaking from the network but I suspect there are one or more users using more than their fair share and I'd like to find out exactly where it is going.
I have recently install Tomato on my E4200, version 1.28 by Shibby, you should definitely look at that, seems to run well.
What you want are K26RT-N, which supports 5Ghz as well.
Here's an even more direct link to latest (Build '101')
You can get the AIO build, which gives you everything. I can pretty much guarantee it will meet your needs.
EDIT: I think these are for the V1 version of the router, not sure about the newer V2's.