Are you uploading stuff from your other computers? If you're taking up more than 90% of your total upstream bandwidth, you'll slow your download speed WAYYY down. So your network as a whole can upload 30 kB/s, than you can't upload at more than 27 kB/s (including all the computers in your network). And the official BT client ain't bad, but it's kinda outdated and a pain in the ass to deal with. But anyways, play with your bandwidth a bit and see what you come up with.