I was recently upgraded from 4mb cable bb to 10mb , my isp is Virgin (formally NTL).

To test the speed, i have visited various speed test sites.

They were:
www.speedtest.net
www.speedtest.bbmax.co.uk
www.thinkbroadband.com/speedtest.html
www.broadbandgenie.co.uk
www.numion.com

Out of all of them, only numion prvided results expected from a 10mb line, roughly around 9.5mb. All the others differed , between 4.5 and 5.5mb.

I spoke to Virgin and they said that because i got a good result with numion that as far as they are concerned the connection is fine.

What would cause this? Are they correct? Are these speed test sites reliable, if not what is the best way to test connection speed?

Thanks

Keep in mind, network congestion can and will affect your connection rate. So if you're connecting to a busy server during a busy time of day, your results will differ from if the server's not that busy and the network load itself is light.

If you're really concerned, run tests on each site and vary the times of day you run them. Do that over several days and keep track of what you get for estimates from each server and then compare the average of each with the others.

Also keep mind that your ability to download at 10mb does not mean the website will upload to you at 10mb.
And, speed is in two parts; bandwidth and throughput. Your bandwidth is your theoretically maximum connection speed. But your throughput is your actual data transfer rate after the overhead of trasnmitting the data takes affect, which is typically anywhere from 20% to 30% of overhead.

So you may have 10mb of bandwidth, but your only going to get about 8mb or less of actuall throughput, and that's only if the other end is capable of sending that fast.

Assume that I already did an Internet search.

Having ran several tests throughout the day from various sites (the ones listed) as well as Dan Elwells broadband speed test.

They all, apart from numion, result in speeds between 4.5 and 5.5mb.

I am really not sure what to do, on the one hand virgin claim that nothing is wrong since numion is saying that i am on 10mb, yet no matter what other site or tool i use it says that i am not.

I realise that i am not going to get 10mb, yet i think 4-5mb is a little slow. So taking into account overheads is really should expect a bit more.