I got 8-9Mb from my Sammy 2100 after they fired up 20Mb in my area (I was on the 10Mb) service, but swapped to a modem to make the most of the upgrade to 20Mb, I'm getting 18-19Mb fairly consistently now through a 255 modem - guess I'm one of the lucky ones.
Probably far to many variables like is your area oversubscribed and have you got a well built STB for this to be an accurate example for you though.