True Net's results — which the Commerce Commission uses for its monitoring — showed a comparison of the average and maximum speeds from 720 tests at each site.
True Net testing expert John Butt said most consumers were not getting close to what was promised to them.
In July, at 35 of the UFB sites, consumers were paying for the fastest UFB option available — download speeds of up to 100Mb/s. Results showed just six of those customers were getting between close to or more than that, a further 17 were getting over 90Mb/s and the remaining 12 were between 30Mb/s and 80Mb/s.
An Orcon spokesman said the service was "like a motorway that slows down in rush hour" as multiple users connected.
"The stated speed is the speed cap placed ... "
Telecom spokeswoman Lucy Fullarton said the company delivered the fastest possible speeds it could to its customers. A Vodafone spokeswoman said the company used its own testing agency and was happy with its results.
Internet NZ Work Programme director Andrew Cushen said he understood it was hard for ISPs to deliver consistent speeds, but consumers were entitled to more information before signing up for the deals.
Minister for Communications and Information Technology Amy Adams said Crown Fibre conducted stringent testing on the main network, and would investigate any contractors delivering substandard speeds.
Neighbours' internet broadband services worlds apart
Miriam Bell and Damon Fee connected their Grey Lynn house to the UFB network just two and a half months ago, but their neighbours, Kevin and Eva Lin, will not get the service until 2016.
Ms Bell said the couple were sick of slow broadband and jumped at the chance to have the speedy service installed.
"Our connections before were not very good," she said. "We had major problems, it cut out a lot. It used to be situated in my study and the wi-fi didn't reach the whole way around the house, for example, but now it even reaches out to our sleepout, which is cool."
Ms Bell, a writer, works from home and uses web browsers constantly for research. Her partner uses it for gaming and entertainment. She said the couple were offered a deal just $10 more than they previously paid.
Over their back fence on Shirley Rd, Grey Lynn, Mr and Mrs Lin spent up to six hours each evening online watching movies, television shows and communicating with friends and family on their ADSL service service.
Mr Lin said they would prefer to be connected to UFB but their address did not qualify for the service until mid-2016. "We would like to improve if we could. We are from Taiwan and internet over there is really well developed ... it's just so much faster."