Your download speeds are sometimes directly affected by the seeds that you connect to. If you are running any kind of firewall then you are somewhat limited as far as who you can connect to. You can only connect to locals who are generally slower in terms of their uploading bandwidth, thus your limited downloading bandwidth.
By forwarding the port used by Azureus in your firewall you will then be able to connect to remotes which usually have higher uploading bandwidth so it becomes possible to achieve higher downloading speeds.
300Kb is not that rare, it fact for me it's quite common. I usually consider 60-100kb a slow download and I'm usually tempted to terminate it. I also find that limiting my upload bandwith leaves more bandwidth for downloading.
The image below is an idea of what my then 3MB Comcast connection delivers on a regular basis. Comcast has now upgraded to 4MB, no charge.