From what I read here, the difference is very slight: Pro will get you BETTER sources, meaning that you'll have better chances of completing the download which in turn makes the download "faster", "faster" NOT refering to actual download speed.
I guess you could say that it doesn't make the downloads faster but rather (if you use is right) reduces your chances of getting an Awaiting sources status (reduces, not eliminates).
If you want truly faster downloads in terms of actual speed (kbps) then it's up to you to get a better connection.

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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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