I presume you're in the UK if you're looking at BT Rapid?
There's a couple of things to consider, how far you are from the exchange, the quality of the line etc.
Remember that regardless of which ISP you are with and what they potentially promise, the line from your house to the exchange is likely to run over a bt line if you're looking at copper service.
.. but, to give you an example, I'm about three miles from the exchange, my line is with BT but from the exchange onwards I hook up to an O2 service.
Up Speed: 2047 kbps
Down Speed: 5849 kbps
Although I subscribe to the O2 service, I believe they actually lease or resell the service from bethere.co.uk.
The pros are if you have an O2 mobile, they give you a reduced service taking it down to about £14 a month with a static IP.
The cons are it took me a week to convince them they could give me a reverse DNS lookup and they can only give you one static IP.
I'm considering moving to their parent bethere.co.uk who can provide more IPs and promise they don't impose traffic shaping etc. bethere has a service for about £24 a month. The only thing holding me back is I'll have to change all my DNS IPs...
It's worth your while asking BT to run a diagnostic on the line for you.
Hope this helps.
If anyone else knows any good UK ISPs I'd be interested.