Hi ModemMan, welcome to the forum (checks profile and see's that you're a long time lurker rather than poster).
I had a similar bonus a while back when I was trialling the higher speeds from the Dunkirk mast. I can't remember the upper limit but it was certainly higher than the VMax 24mb/10mb package I am on now.
I only noticed after I uploaded a lot of photos and videos to Flickr and it finished much sooner than I had expected. Speeds were set back to the fixed package a month or two later.
I reckon they are giving us a free hit to get us hooked
Downstream ~24336.33 kbit/s - ~2970.74 KB/s
Upstream ~10224.86 kbit/s - ~1248.15 KB/s