Streaming is old hat
I just download from iPlayer, never stream.
I have "8Mb" ADSL.
If I try to download at 6pm, it takes about an hour for an hour programme.
If I try to download at 6am, it takes about 20 minutes for an hour programme.
The main thing to bear in mind in terms of bandwidth caps and streaming, is that they aren't related. You may be allowed 40GB in a month, but you can't have it all at peak times, and this is a completely fair arrangement on the ISPs part.
They've said "up to 8Mb" and they've said "bandwidth allowance = 40GB" but they never said "8Mb speeds at all times" - that's what paying more money gets you, hence I don't, and download iPlayer programmes.
Surely the point of catching up, is you're less restricted to when you want to get it, so why the huge desire to stream? Downloading the files makes the content caching solution more viable too. ISPs should pay for this in partnership with the BBC. They pay for it, and thus protect their networks.