Well, they don't necessarily have to wait: if another source has the files you serve and they are able to connect to it, then it's ok.
It goes without saying though, that the more sources, the better.
When I check my uploads, if there's only one user uploading, they'll usually get around 11KBps. More than one upload means less upload bandwidth for every user: how many users are you uploading to (on average)?

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

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