Your connection time is only 3 hours which I presume is because you changed from the HH5 to the Smart Hub. Your noise margin is slightly high so there is slight room for improvement in your connection speed.
You should leave the SmartHub connected and if the line is stable your speeds might improve slightly.
As regards moving your hub out of the cupboard. That would be the best thing to do because obviously the wireless signal at present has to go through the walls and door of the cupboard before it goes any where else however for the slight, if any increase in speed you would get it would probably not be worth paying £130 to have that done.
Your speed is dictated by your distance from the cabinet you are connected to. The speed drops of over distance. See graph.
The problem is not your Internet download speed.
The problem is not your broadband connection, if you are getting speeds of 25M download.
It is not a fault about what cabinet you are connected to. You get connected to the nearest or the cabinet that Openreach deem is the best for you and you can not change to another cabinet.
There is nothing you can do about the noise margin. It is just a measurement of how your line is performing and can fluctuate for a number of reasons. If you don't disconnect your Homehub it might improve.
As others have said it is not your broadband speed your browser "Safari" should open even if you have no broadband connection.
It would not work of course.
Do you have a smart phone or other device that will connect to the internet even by WiFi and see what the speed is like, with the slowness you are experiencing you don't need to measure the speed just see if it seems faster.
I assume you have a mac which I know little about but is there any diognostics built in.
I think your problems will be with the computer rather than the broadband.
There could even be a dodgy app that is hogging all your processor speed.
Thank you. I will check using iphone 5 which I must admit is relatively faster than my own iphone 4. Maybe I just need a new macbook. I don't have many apps to worry about but you never know. I can see my wallet being lighter this weekend as i think I'll buy a new macbook, mine is getting on a bit and may be the problem. But in my defence, BT does go on and on and on etc, about how fast they are, but it depends on a number of factors no doubt. Maybe Gill Gates will reduce his prices rather than saving the world just for me this weekend! Not.