In my opinion, the speed chart was quite helpful.
AFAIK, the tracker software can not cause a sudden drop in upload speed, as a result, I can not comment on how you are having problems with BakaBT tracker only.
Takeshi's advice can help you configure your bandwidth, or you can use Speedtest.net (which most of us use i guess) to gauge your internet speed. I suggest that you test your connection while the upload is trailing low and select a server outside Greece (like France or Germany) for proper measuring.
If the result does not indicate a problem (matches with your subscription) then a sudden drop in upload speed while you are fully using your upload bandwidth might be the result of the following
- your connection is throttled, you can use the encryption feature of utorrent > Preferences > BitTorrent > Protocol Encryption
- utorrent still has bugs, just set a upload cap below %10 of your original upload capacity (70 kb/sec)
Also there are members with more experience on utorrent, so you can wait for an answer from them.
good luck