i'm also on the shaped 4mb and seems on my line during the day i get 100-200kb on usenet using astraweb, around 7 at night it drops to 30kb then around 10pm picks up to full line speed, but the shaping is 24/7 not just weekdays. I have noticed that you need to play around with your nzb settings, if u using astraweb try using the ssl username option and ports provided with them, the speeds should increase, everytime i use the plain astraweb nzb name on port 119 the speeds stay on 30 so those ports are being shapped a lot, HTTP runs between 200-350kb 24/7.
Torrents i wont even worry cause almost everything is on nzb lately before torrents.
Then friand of mine is also the same ADSL 4mb and same package and he gets full speeds and very happy and they use a megaupload account, so i recon it might also be your exchange area that plays a part in the speeds we all getting. but realy want to test mweb aswell sofar only good things are coming from them