Officially Rogers wants you to have a DOC3 modem for speeds 18mb and above, but I'm with Distributel ,and I've had my old 5100 for years it continues to provide from the lowly 5 or 7mb when I got it all the way up to the 28 today.
You don't need DOC 3 for 20mb, I'm currently pulling 28mb on my DOC 2 modem just fine.
If that's the case I would be super happy, I would like to hear form Rocca though to be sure because in Cogeco land it's considered Doc 3. If your city is not upgraded you cannot get it.