[FTTC] Poor/inconsitant speeds/connection drops since unlimited upgrade

[#1]

I joined PN  in november on the Extra fibre package and was enjoying a stable connection with fairly consistent speeds of 70+/16 Mbps (IP profile of 78Mbps) and ping around 20 ms
This may be coincidental but,
I decided to upgrade to unlimited which completed on 20th feb and have since suffered several connection drops, and speeds that range anywhere from around 16 - 60 mbps and latency has increased to 40+ ms
I've done a quiet line test, which is quiet as a mouse and can make/receive calls ok, so not an obvious line fault
I've also connected my PC directly to the BTOR modem to eliminate router/network faults and was seeing the same inconsistency.
My connection is actually fairly stable today and getting around 50 - 60Mbps
I've run a BTw further diagnostic test again today and notice my ip profile has now dropped from its previous 78Mbps to 69.86 Mbps (presumably as a result of dropped connections/instabilty and why its now stable)
Results of the test,
Download speed achieved during the test was - 53.64 Mbps
For your connection, the acceptable range of speeds is 16 Mbps-69.86 Mbps .

Additional Information:
IP Profile for your line is - 69.86 Mbps
Upload speed achieved during the test was - 10.45Mbps

Additional Information:
Upstream Rate IP profile on your line is - 20 Mbps
PN still has my profile at 78Mbps according to https://portal.plus.net/my.html?action=data_transfer_speed
Estimated line speed:
75Mb (Accurate to within +/- 1Mbit) - Checked on 2013-01-22 23:54:43
Current line speed:
78 Mb
So are the current speeds what i should now expect, as a result of the unlimited package or do i have a fault?

[#2]

The speed/high latency issues (if they are at peak times) could be related to this thread - http://community.plus.net/forum/index.php/topic,111170.msg964808.html#new

[#3]

Was aware of the peak time latency issues, but it wasn't just at peak times i was seeing problems. Though as i say as of today its currently stable albeit at lower IP profile/speeds

[#4]

Hi there,
There's no way an account change would alter your sync speeds or line profile, those are controlled entirely by the equipment at the exchange and green box, the wiring between there and your premises, and your own router and wiring. If you're noticing the connection dropping (which is often the cause of speed changes like these) best thing to do would be to raise us a fault at http://faults.plus.net - that'll send a ticket to our faults team once all the questions have been answered, and they'll get it sorted for you.