The upload and download rate aren't the bottleneck, vegetaleb.
What slows you down in this case is the number of open connections and even after you finish the download and stop seeding, many of those remote IP addresses will still be poking at your connection (hence the 30 minute slow down you are seeing).
What slows you down in this case is the number of open connections and even after you finish the download and stop seeding, many of those remote IP addresses will still be poking at your connection (hence the 30 minute slow down you are seeing).