Mate, you've made a huge mistake going to Sky Connect. Whilst Sky LLU offering is amongst the best, it's BT based service (Connect) is one of the worst. The symptoms you describe are classic Connect symptoms : line speeds during non peak hours and significantly lower speeds at all other times. Are you tied into a contract with sky? Might be a good idea to go back to BT.
TalkTalk Plus LLU ADSL2+ connected @ 18015/1019 kbps
Attenuation 27db down / 9db up
Noise Margin 2.9 db down / 12db up
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