Another thread?? Take a deep breathe and exhale.......
Usenet - cheap doesn't mean good. You need to look at a couple of things:
1) Retention - how long do they hold the posts? I've seen some places quoting 1000 days but then they have crappy completion....which leads on to the other thing
2) Completion - what percentages of their files are complete. Have 200 day retention with near 100% completion is better than 800 day at 50%.
Not having 100% completion on Usenet is not a problem thanks to PAR files, but obviously you'll want as much as you can.
Now, as for the throttling. There are possible ways around some throttling.
On Virgin Media if used NNTP port 119 or secure NNTP port 563 then you'd get throttled, but if you found a provider with access over port 443 VM though it was HTTPS traffic and didn't throtte.
You will need to find out specifically what BT throttles and what people using Usenet on BT are doing.
2 good providers off the top of my head are Astraweb & Giganews. You tend to find people love one and hate the other!! I used Astraweb a log time ago and it was good. I can't comment on Giganews.