Gradual speed decrease NORMAL?

[#1]

I've had my fibre unlimited service now for 8 months.
For the first half of this term I used to get 58mbps down and 15mbps up however the later half of this period I've found the speed decrease to 48mbps down and 9mbps up.
I am certain at its not an issue with the line as the line was newly fitted with my fibre connection. I've also had my equipment recently replaced (unrelated issue) by Plusnet.
I have spoken to Plusnet support and they claim this is 'normal' and they cannot do anything.
Can anyone suggest what I should do next? And is what Plusnet has said correct?

[#2]

I think some speed decrease can happen as more people on your cabinet switch to fibre, then there's more crosstalk, which is the signal in one line interfering with the signal in another, reducing the attainable speed.
At some future date, "vectoring" technology should be rolled out (or enabled) which reduces that problem. I think Openreach are trialling it in a couple of places.
Also, does it really matter that much? What can you do at 58Mbps that you can't do at 48Mbps?

[#3]

Mine has gone from 73Mb when installed to around 65-68Mb after 7 months of use - it seems fairly stable at this speed now and is still above the 50.4Mb estimated for my line.

[#4]

The download speed decrease doesn't bother me too much I guess but the upload speed has gone down by a third so there's a noticeable difference when uploading files to remote locations.
I thinks by the time copper vectoring is widely available FTTP will be here.
Gonna wait and when FTTP is available from PN, hopefully them I should get the full speed.

[#5]

seems to be allot of people suffering the same speed drops, I'm just wondering if the network weather it be Plusnet or the core BT network can cope with the increase number of people using it or if it could be a ploy to reduce the overall bandwidth of downloads since unlimited was interduced to the Fibre networks. It costs providers the more traffic that goes across their network so more people downloading more with no caps pushes up costs so reducing speeds can help reduce these costs. I now see BT are reducing the estimates on lines which a year ago for example where estimated at 55Mbs are now 39Mbs, try testing via BT ADSL Checker what you line estimate is now to what you where quoted at install.

[#6]

I suppose this article may be of interest regarding how much of a speed decrease could be classed as a fault.

[#7]

I've taken a look over your connection and can see no issues although your sync speed it higher than the speeds you're reporting.
Are you connecting over a wired or wireless connection?

[#8]

The down speeds are still correct.. however I've found the upload speed has fluctuated since I last checked it.

[#9]

As asked above though, are you using a wired connection to the router or a wireless connection ? It can make a huge difference.