Hi. I am also a Blueyonder 10MB customer and like you was disappointed to see no apparent improvement in speed. I pursued this vigorously with Blueyonder (OK so I had some time).
The outcome was this: you will not perceive extra speed but you will be able to run many more concurrent downloads.
I tested this using their servers, downloading multiple instances of very large files. It is true to say that I could run many more concurrent downloads before the speed of download started to slow.
However, my non-technical view is that this is a bit of marketing bulldyke. Double my bandwidth suggests really fast performance. There is little realworld benefit.
Like you also, I think I would rather have an upgrade to the upload bandwidth. This would make video conferencing hum.
Anyway, hope this makes you feel a little less swindled.