Interesting. My brother has the Ultra HD box as he has fibre too and so got a full package however my parents have the standard box and tbh we haven't noticed a huge difference. Error or issue then maybe? Not great either way.
And YouView is slowly starting to get there from the looks of it. Will be interesting to see once the update drops and can compare again but for now my opinion is still that at least the Sky UI is significantly better and more sleek than any other service provider be it through TV, Online or box.
I guess thats where I can tell the difference more. If I use the HD box then go use the Ultra HD box the latter is noticeably quicker.
Really Sky's UI should be a lot better they have had more time to develop one where BT just nicked Youview's and bolted on a few extras like the BT Player which is not very good anyway.