As I've said above, your BT speed is not limited to 5Mb/s in Harringay. The availability of superfast broadband is determined by which BT exchange you are connected to, and as far as I'm aware, the Harringay ladder is all served by the Crouch End exchange (which can deliver superfast). If the BT website is telling you 5Mb/s, this is likely to be an error in its address database (which could be resolved by a phone call).
I did speak to them a few years ago and was told that was what the speed was. The blackspot seems to be around the N8/N4 border at the Green Lanes end (Allison, Hewitt, Seymour kind of area).
So far as I'm aware it's not proper fibre that BT offer on the ladder, it's fibre to cabinet and then copper line to the properties. I assumed that the blackspot was due to a gap between the cabinets.
For me FTTC is too slow anyway so I've not looked into it too deeply.
I suppose it's conceivable that there's a technical issue with a street cabinet somewhere or something (although if this was a "few years ago", I'd be surprised if things haven't moved on). My basic point was that BT's address database is pretty rubbish, so I wouldn't rely on that alone to give an accurate picture of service availability, given that we're in a SFBB exchange area.
You're also right that it's not fibre to the premises, but fibre to the cabinet is a "superfast" 50-100Mbps service, more than enough for most people's everyday needs.
Yes, it may well be a database issue (although I would be a little concerned about a company that's had errors in its database for 5 years plus and hasn't corrected them).
Agreed, fine for general browsing, etc. The issue for me is when the xbox decides to download a 7GB update or game, I can't imagine how people use them without fibre.
It doesn't take long to download 7GB over normal superfast (@50Mbps,say). But maybe there's a gaming-specific reason you need it faster than the couple of minutes that would take.
7GB @ 50Mbps in a couple of minutes? Not likely.
Sorry, my mental arithmetic was off. Over BT's faster service (100Mbps)it would be about 10 mins I think. Fact remains that for 90% of people 50 or 100Mbps is absolutely fine, and switching to a faster service isn't going to make a material difference to their experience.
If you are looking at a non Virgin service, I can't recommend Zen Internet highly enough. 1 issue in 7 years (Openreach engineer screwed andup) it was fixed the next day.