Why does the Plusnet IP profile affects speeds so much

[#1]

This may seem an odd question but ever since moving to the new unlimited product the Plusnet profile was stuck at 7.15Mb
Yesterday - on the Plusnet site - it dropped to 4.3Mb
Looking at my router log the actual change happened at 1.45 this morning
Now my sync speed is 4896kbps with an IP profile of 4312kbps
So you wouldn't expect much of a change in speed test results but - as can be seen in the attached picture the speeds dropped from about 4230kbps to about 4070kbps
As a secondary question - why did the automatic systems take so long to update the connection after the figure changed on the website (noticed at about 11.50am yesterday)

[#2]

Sorry Jim, is the question why has the speed dropped by 160Kbit following the change of the PN profile?

[#3]

That is correct
Also you may not have picked it up but the automatic systems are supposed to update the connection within an hour or so from the information being received from BT but in my case it took well over 12 hours after the website updated

[#4]

Quote

the automatic systems are supposed to update the connection within an hour or so from the information being received from BT

The speed change won't be applied until a PPP disconnect/reconnect happens. This should be forced shortly after the change but doesn't seem to always happen.