As MHC has indicated, the actual contract will almost certainly be qualified by "Up to ..."
However, I recommend that you do Quiet Line Tests, to ensure that your Land Line and your internal phone extensions (if any) are "clean".
Using preferably a corded phone direct in to the NTE (the box where the Exchange Line terminates within your house)
Option 2 (or SKY Option 4)
A very low, quiet hum is usually acceptable.
Anything louder, "Snap, Crackle, Pop) dialling tones, test tones, bangs etc are not acceptable; and should be reported to your (Voice) Telephone Provider - NOT mentioning Broadband.
The legal requirement applies to Voice Telephony only, even if you otherwise "only use my mobile", which you also should not mention.
Also QLT from any extensions and if (more) noise is heard, there is a problem with those extensions.
These tests should be with your various phone devices such as BB Modem/Router etc both disconnected totally and then plugged in and ON, progressively, to enable you to identify the source.
First time around may take you about 30 minutes; but could be time well spent.
Without a "clean" Land Line and internal extensions, you are never going to get "best performance".
It is your responsibility to sort out any problems in that area.