Nice plan... (wish I lived there)
Anyhow... with respect, your question is largely irrelevant, 1Gb to the home is a ridiculously fast connection. most web sites and places you are likely to download from won't be able to keep up with your connection so there will be a bottleneck at the other end, not at your end.
Also... the main internet connection is 10Gb with nearly 1500 homes sharing it, so potentially you would never get the whole 1Gb to your house available as bandwidth to the internet yourself because it's shared (this isn't as bad as it sounds as sharing a connection is the standard way of dealing out internet connections and due to reasons I won't go into because of lack of space here.... it works better than it sounds like it will)
Just pay the £30 a month and be happy with what you'll be getting, it's far better than pretty much anyone else in the UK.... speeds of over about 10Mb become pretty much irrelevant for one computer for most purposes anyhow, once it gets to much higher than that the main benefit is that you can have more than one computer running at once on the internet.