Hi and welcome.
The post office use BT Wholesale products, which are used by many other IPStream ISPs such as Zen, Plusnet, IDnet, Enta etc erc. Its up to the ISP how many users they load on a pipe, and if theirs too many users, then you get ISP contention and slower speeds as per say the Tiscali IPStream.
IPStream BTw bandwidth isnt cheap and it costs the ISPs therefore they have to decide how they manage how much the user can download... some ISPs use straight forward CAPs of xGB, others may throttle back certain applications such as p2p.
Theres a list of
ISP prices and caps and also a list of
ISP performance on the main site.
As regards to the Post Office, little information has been forthcoming but I suppose the main thing is that I havent seen (m)any complaints.
Try having a look on the main site at users comments on what they say about their ISP and how they rate it. -
ISP ratings.
Select the ISP from the drop down box to see user comments