I would suggest sending an e-mail or giving Atlantic Nexus a call. From what I have seen of their customer service they would be more than happy to discuss the network with you.
I can say that the connection after leaving your CO will be on the Atlantic Nexus network. I have been using them for sometime and could not be happier. Over the years in Atlanta I have used Bellsouth, Charter, Sprint (No longer in the biz here)Speed Factory and Speakeasy. As far as networking with all these carriers and congestion slow downs I would have to say that with the exception of Sprint's Business Class Service and Speakeasy SDSL service that Atlantic Nexus has the next best network I have used.
Also out of ALL the above carriers the Tech Support at Atlantic Nexus is 2nd. to NONE! I have dealt with a lot of companies and I have never see such far superior tech support with anyone else. ( This is if you ever have to use them) Atlantic Nexus uptime here at my residential service has never been down more than 2 hours in two years and most likely that was Bellsouth's copper or a CO problem.
I have never had Comcast, but my Girlfriend in Alpharetta does. I can tell you that she calls me at least every two weeks that her connection is down. They have a TON of problems with their DHCP servers not handing out an IP address. I spend a lot of time with her ruling out it being on her end. Now call Comcast support and they do not even know what a dhcp server is but they will send out a tech to exchange out the modem and then they reverse trouble shoot. I will say that when they are up they are fast. But darn sure not reliable for my use.