The SB4100 according to Motorola's own specifications sheet here
http://broadband.motorola.com/modem/SB4100.pdf is capable of upto 38mbps down and 10mbps up so should be able to easily cope with whatever NTL throw at it. I personally believe that there is a configuration issue at the moment that as yet they havent ironed out. But personally I'm happy with the 5.5mb I'm getting and will sit back and wait to see if it improves over the next month before getting my knickers in a twist over it.
