me d
Your your UL speed will affect your DL speed what are your speed test results. From what I can make out from your post you have around 300KB/s down and 75KB/s up
Now the test that I have been running lately show that if I am downloading from 60 host at 600KB/s to 750KB/s and have UL at 0 that it take 20KB/s to 25KB/s UL for communications between my computer and the host I am downloading from. Your computer has to tell every host you are DL from that it received the packet and is ready for the next it has to have UL bandwidth to do this.
Now you have your DL limit set at 12 and lets say you have 10 host for each file 10 X 12 = 120 host. The test I have done says it takes a average of around .33 KB/s per host for communication between the computers 120 X .33 = 39KB/s UL bandwidth needed to DL from 120 host. If you are UL at 50KB/s then you would be slowing down your DL capabilities because you have to wait for UL bandwidth to communicate with your host.
I do not know that these numbers are absolute I do know that they are right for my DL scenario.
http://www.dslreports.com/speedtest?more=1