I did the $10 a month upgrade to go from 4 megabits to 6 and heres my score:
Connection is:: 6127 Kbps about 6.1 Mbps (tested with 5983 kB)
Download Speed is:: 748 kB/s
Tested From:: http://testmy.net/ (main)
Test Time:: Thu Apr 21 11:35:05 MDT 2005
Bottom Line:: 109X faster than 56K 1MB download in 1.37 sec
Diagnosis: Awesome! 20% + : 81.92 % faster than the average for host (Comcast.net)  WHOA!!!

After doing the upgrade to 6Mbps I could no longer use a cheap generic router for my very small lan.  I own my own home based business and I could not believe what I learned from this experience.  DO NOT USE A BARGAIN ROUTER if you are going to use ANY higher speed than 4 Mbps.  Most routers are 10/100 yes, but the WAN port only can usually utilize under 4Mbps.  I returned it and bought the White 4 port router with built in 802.11g wireless and this thing rocks.  As you can see by my results it works awesome.   The generic one I returned showed my connection at only 4.3Mbps...  eeks...