jkmullins

Here's the page straight from the source:  http://www.dd-wrt.com/wiki/index.php/Version_5_And_6_Router_Information

Looking at that, it is not easy to do, and there are problems running even the Micro on a low memory device, but it apparently can be done.  The prevailing recommendation is to get a pre-v5 G/GS or a new GL.  I got a GL just for the purpose of running DD-WRT and it's working great.

I worked at a cable ISP, and the explaination is simple.  You are never going to exceed the cap set on your modem, and the cap can be set down to the kbps, however, most ISP's, for their top tier plan, uncap the downstream and allow the modem to get anything it can.  They keep enough bandwidth to make sure everyone is getting the service advertised, and when they start getting close to the limit, they'll buy more.  When the buy the extra, everyone on the highest tier will see a speed boost that will fade over time as demand continues to rise.  Then the ISP will buy more bandwidth, and the cycle will repeat indefinately.