Depending on your provider, the Motorola Surfboard download and upload speeds are well documented on the technical specs for the Motorola Surfboard SB5101. Don't forget to do a speedtest as well. Some claims from ISP's come in that the modem is limited to 12-10Mbps Download and 500-512Kbps Upload speeds. This doesn't necessarily corrolate with numbers you could be getting in real time so check with speed networks available online (google search string: upload speed test). Though it is a DOCSIS 2.0 the PDF clearly states 30Mbps (Max) Upload (Upstream) and 38Mbps DOCSIS 2.0 (EuroDOCSIS 2.0 51Mbps ) download good for up to and a bit over the mid range packages. If you get less then what your subscribed package claims, it might not be the modem but other factors within your neighboorhood.
In other words, before you sign up for any new plans or purchase new modems be sure to check your modem limitations and current speeds.