Don't understand why current speed is so low

[#1]

When I look at the High Speed Broadband page in the PlusNet member centre it reports:
Estimated line speed:
    41Mb (This may vary between 31.7Mb and 41.4Mb) - Checked on 2016-02-14 10:25:43
Current line speed:
    25.4 Mb
25.4 Mbps isn't anywhere near the estimated line speed being well below the minimum quoted. Is something wrong or am I just misinterpreting the figures?

[#2]

Run the BT diagnostic speed test and check what speed it gives for your IP Profile

[#3]

It gives 25.44 Mbps which I think is about what the line can give at this distance from the cabinet. My query was why the line estimates are so much above this?

[#4]

The line estimate is often rubbish but should come from here http://www.dslchecker.bt.com/adsl/ADSLChecker.TelephoneNumberOutput
Mine shows a value in the middle of the clean range

[#5]

Thanks for the comments. Oldjim's link gives the following:
                                                          Upstream      Downstream (Mbps)
                                              High Low      High Low
FTTC Range A (Clean)         35       27.1 7.6 5.8 -- Available
FTTC Range B (Impacted) 27.3 13.5 6.2 1.4 -- Available
I guess my line must be "impacted". What a pity that BT don't replace suspect copper - preferably with fibre.

[#6]

Even on a good day you wouldn't get 41Mb looks like the max your line can go is 35Mb...and that would be in a perfect world.

[#7]

Sadly I only get 24.5Mbps.

[#8]

The puzzle is where the Plusnet estimated line speed has come from!

[#9]

It's not uncommon for the BT estimates to change mine use to be 67Mb but when my speed dropped it was adjusted it's now 43Mb on BTs end but nothing is listed for Plusnet. 
@Jelv maybe that was the BT estimate at the time the OP signed up but has since been adjusted on BT's end but hasn't on the plusnet side.   

[#10]

Quote from: tallstory

My query was why the line estimates are so much above this?

That would be why it's called an estimate