You're saying that like 55 Mbps is necessary, it isn't. 2 Mbps is required for SD streaming and about 4Mbps for HD streaming, these speeds aren't ideal but plenty of people, and families, do just fine on less than 10Mbps. How many places in the UK can't access broadband at 10Mbps?It should be that quick for everyone. Let's spend money on making the whole country connected to decent internet, rather than only connecting bits of England to London.
It's not about "how much faster", you're asking the wrong question. You should be asking, "why can't the whole country have access to decent broadband speeds?"
Edit: To make it clear, I think everyone should have access to Broadband of at least 15Mbps bandwidth, and there should be costed plans to achieve this where practical. But HS2 doesn't need to be cancelled to pay for it!