I've been on 10MB since january or so and I am one happy chappy with the service.
Peak time I usually get speeds around 800KB/s - 900KB/s which is great, nightime I always hit over 1000KB/s, normally 1.1MB/s.
I think NTL can handle the fast speeds all day long without no problems, but they say this statement to cut costs & make more profit, after all they are a business.